bluuebunny/crossref_metadata_2025 huggingface dataset:
LIGHT AND ELECTRON MICROSCOPE STUDIES OF MORPHOLOGICAL CHANGES OF MITOCHONDRIA DURING SPERMATOGENESIS IN THE GRASSHOPPER
Authors: Tahmisian T. N. , Powers E. L. , Devine R. L.
Published: May 2004

1. Observations on the morphological changes of mitochondria preparatory to the formation of the nebenkern, as well as changes within the nebenkern, are reported.

2. Mitochondria enlarge and divide during the meiotic divisions.

3. The mitochondria of the spermatid elongate, become filamentous, form a crescent, and partially encircle the nucleus.

4. Nodes which develop on either end of the crescent become entwined as they move toward each other.

5. The two nodes coalesce to form a filamentous or early type nebenkern which is described by others as chromophilic.

6. Internal rearrangement and partial dissolution of the filaments result in the development of the late or chromophobic nebenkern which separates into two distinct bodies.

7. The nebenkern moieties send out processes toward the centrosome, and after making contact, elongate and occupy part of the space between the tail filaments and sheath of the spermatozoon.
MITOCHONDRIA OF PROTOZOA
Authors: Sedar Albert W. , Rudzinska Maria A.
Published: May 2004

A study of thin sections of Paramecium multimicronucleatum, Tetrahymena pyriformis, Tokophrya infusionum, and Amoeba proteus shows that the mitochondria in all these protozoa are similar in certain aspects of their fine structure to that described in metazoan cells. As in higher organisms the mitochondrion is surrounded by a double limiting membrane and contains protrusions directed inward from the innermost of the double membranes.

There are, however, some differences. In a majority of higher organisms the internal structure of mitochondria consists of ridges or cristae mitochondriales and in a few instances only of finger-like projections, or microvilli. In all protozoa described here and elsewhere microvilli represent the dominant structure. They are characteristic therefore of protozoan mitochondria.
THE STRUCTURE OF PIGEON BREAST MUSCLE MITOCHONDRIA
Authors: Howatson Allan F.
Published: May 2004

The structure of pigeon breast muscle mitochondria was studied both in whole muscle tissue and in mitochondrial fractions separated by differential centrifugation. No evidence was found to indicate that the mitochondria of pigeon breast muscle differ in any fundamental way from those of other tissues. In particular the absence of an enveloping membrane, claimed in recent reports, was not confirmed.

The structure of the lipide bodies present in muscle has been described, and compared with that of similar bodies in other tissues.
THE ULTRASTRUCTURE OF A REPTILIAN MYONEURAL JUNCTION
Authors: Robertson J. David
Published: May 2004

Myoneural junctions in Anolis are characterized by the formation of troughs in the surface of the muscle fibers in which small branches of the terminal axon lie. The muscle surface membrane lining the troughs is thrown into complex branching and anastomosing folds, which compose the subneural apparatus of Couteaux. A compound membrane 500 to 700 A thick separates axoplasm from sarcoplasm at the endings. This consists of five distinct layers and is described in detail. A thin layer of cytoplasm (probably Schwann) separates terminal axoplasm from extracellular space at the surfaces of the junctional troughs. Terminal axoplasm lacks axoplasmic filaments and contains numerous vesicular or tubular appearing structures about 300 to 500 A in diameter. Both terminal axoplasm and sarcoplasm contain numerous mitochondria.
A STUDY OF CHROMOSOMES WITH THE ELECTRON MICROSCOPE
Authors: Ris Hans
Published: May 2004

Amphibian lampbrush chromosomes and meiotic prophase chromosomes of various insects and plants consist of a bundle of microfibrils about 500 A thick. These fibrils are double, being made of two closely associated fibrils 200 A thick. Fragments of interphase nuclei contain a mass of fibrils 200 A thick. Ultrathin sections through nuclei in prophase or interphase show sections of these double or single fibrils cut at various angles. A comparison of sections with the methacrylate left in and sections that were shadowed after removing the methacrylate suggests that the OsO4 reacts only with the outer part of the fibrils either because it does not penetrate, or as a result of a chemical difference of the inner core and the outside of the fibril. It is suggested that in analogy to the structure of the tobacco mosaic virus the chromosomal microfibril may have an inner core of DNA surrounded by a shell of protein.
STUDIES ON NUCLEI USING CORRELATED CYTOCHEMICAL, LIGHT, AND ELECTRON MICROSCOPE TECHNIQUES
Authors: Moses Montrose J.
Published: May 2004

In this paper, a procedure for correlating electron microscope and light microscope cytochemical studies using immediately adjacent serial thin and thick sections has been described and discussed. This technique, combined with the Feulgen reaction for DNA, has been of particular value in framing and answering both general and specific questions about the nucleus. The results may be summarized as follows:—

Apparent nuclear homogeneity in the electron microscope is not due to loss of DNA as evidenced by positive Feulgen reactions in such nuclei.

Arrangement of Feulgen-positive material in chromosomes, heterochromatin, perinuclear and perinucleolar chromatin, etc., is similar to that customarily observed in the light microscope but this is not necessarily reflected in a cursory survey of the electron image.

Careful comparison of light and electron images shows that fine differences in structure are associated with chromatin localization.

Primary spermatocyte prophase chromosomes of crayfish have been positively identified by their Feulgen-positive nature. Core-like axial structures in such chromosomes have been observed (9) and are described further.

A remarkable feature of spermiogenesis in the crayfish is an elaboration of the nuclear envelope of the spermatid accompanying the formation of what becomes a mass of convoluted membranes in the sperm. In the spermatid, perinuclear chromatin follows outpocketings of the nuclear envelope into the cytoplasm. In the early sperm, on the other hand, although the nuclear envelope is continuous with the system of convoluted membranes, the chromatin is distinct from it and is retained in the nucleus proper by some mechanism independent of the nuclear envelope.

None of the above observations was apparent from the electron microscope images alone; they were possible only by virtue of the correlated cytochemical and electron microscope study of adjacent sections.

The successful use of other cytochemical tests, such as the PAS reaction for certain carbohydrates, in such correlated studies is also described.
CHROMOSOME-NUCLEAR MEMBRANE-CYTOPLASMIC INTERRELATIONS IN DROSOPHILA
Authors: Gay Helen
Published: May 2004

The structural evidence for nucleocytoplasmic interrelationships observed in electron micrographs of salivary-gland cells of third instar larvae of Drosophila melanogaster has been reviewed. It has been found that the characteristic nuclear membrane outpocketings with their adjacent highly differentiated chromosomal materials occur at one stage of larval development at a time when a new cellular function is being initiated. Preliminary cytochemical studies to characterize the materials transferred from nucleus to cytoplasm indicate that deoxyribonucleic acid occurs within the blebs. Observations on chromosome and nuclear membrane structure are also presented.
INTRACISTERNAL GRANULES IN THE EXOCRINE CELLS OF THE PANCREAS
Authors: Palade George E.
Published: May 2004

Dense, homogeneous granules of 250 to 350 mµ in diameter have been found inside the cavities of the endoplasmic reticulum in the acinar cells of the pancreas of the guinea pig. They apparently correspond to the fine granules described in the same material in light microscopy by Mankowski and Bensley. The location of these granules indicates that the endoplasmic reticulum is a cavitary system and suggests its participation in secretory processes.
FURTHER OBSERVATIONS ON THE FINE STRUCTURE OF THE MACRONUCLEUS IN TOKOPHRYA INFUSIONUM
Authors: Rudzinska Maria A.
Published: May 2004

In a previous paper (8) an organized structure was described in the macronuclei of certain old organisms of Tokophrya infusionum. It was found that the same honeycomb structure appears in great abundance in the macronuclei of overfed organisms. This permitted a better three-dimensional reconstruction of the described structure.

Since the defined structure may be experimentally induced, it offers an opportunity for further more detailed studies as to its nature and meaning.
THE NISSL SUBSTANCE OF LIVING AND FIXED SPINAL GANGLION CELLS
Authors: Deitch Arline D. , Murray Margaret R.
Published: May 2004

Living chick embryo spinal ganglion neurons grown from 1 to 4 weeks in vitro were studied under the phase contrast microscope. In the peripheral cytoplasm of the earliest stages studied, a homogeneous, phase-dense material is seen which corresponds in location to the cytoplasmic basophil material of the same stages. As maturation proceeds, this material increases in extent, and becomes separated by lighter channels into discrete bodies.

Short fixation by 1 per cent buffered osmium tetroxide followed by post-fixation with neutral buffered formalin does not significantly alter the size, shape, or distribution of any of the cytoplasmic components, and the fixed, hydrated cell is almost indistinguishable from the living cell. Dehydration causes some shrinkage of the fixed preparations, but if the photographs of the stained preparations are enlarged to correspond with those of the living cell, excellent correspondence can be made between at least the larger basophil masses and the larger dark masses seen with phase contrast. Fixation by a formalin-mercuric chloride procedure also results in satisfactory correspondence between the stained Nissl bodies and the phase-dark homogeneous areas. It is concluded that discrete Nissl bodies preexist in the living neuron and are essentially unchanged after good cytological fixation.

Evidence is also presented of the presence of neurofibrils in the living state.
EVIDENCE FROM ELECTRON MICROGRAPHS FOR THE PASSAGE OF MATERIAL THROUGH PORES OF THE NUCLEAR MEMBRANE
Authors: Anderson Everett , Beams H. W.
Published: May 2004

1. The nurse cells of Rhodnius possess nucleoli that stain with Heidenhain's hematoxylin but give a negative Feulgen reaction. In localized positions adjacent to the nuclear membrane are seen masses of material both within the nucleus and the adjoining cytoplasm that stain with Heidenhain's hematoxylin, but, like the nucleolus, give a negative Feulgen reaction.

2. Electron micrographs of the nurse cells of Rhodnius reveal the nuclear membrane to contain pores approximately 400 A in diameter.

3. In electron micrographs the nucleolus is seen to be composed of a reticulum containing tightly packed granules. Between the centrally located nucleolus and the nuclear membrane are observed relatively small bunches of granules of the same relative size as those occurring in the nucleolus. Aggregated at certain positions adjacent to the nuclear membrane both within the nucleus and in the adjoining cytoplasm are irregularly shaped masses of granules. Certain of these masses within the nucleus are seen to be continuous with those in the cytoplasm through narrow isthmuses of material extending through pores of the nuclear membrane. Other masses of granules show evidence of preparing to enter the pores by projecting tongues of material toward and into them. In the adjacent cytoplasm pear-shaped masses of granules are seen in front of and in contact with the pores which suggests that they were fixed in the process of or just after completing passage through the pores.
ELECTRON MICROSCOPY OF THE NUCLEAR MEMBRANE OF AMOEBA PROTEUS
Authors: Greider Marie H. , Kostir Wencel J. , Frajola Walter J.
Published: May 2004

An electron microscope study of the nuclear membrane of Amoeba proteus by thin sectioning techniques has revealed an ultrastructure in the outer layer of the membrane that is homologous to the pores and annuli observed in the nuclear membranes of many other cell types studied by these techniques. An inner honeycombed layer apparently unique to Amoeba proteus is also described.
THE ELECTRON MICROSCOPY OF THE CHOROID PLEXUS
Authors: Maxwell David S. , Pease Daniel C.
Published: May 2004

1. The choroid plexus of the rat has been studied in detail by electron microscopy. Samples from the frog, rabbit, and cat have also been examined without noting significant differences.

2. The surface of the ependymal epithelium is covered by pedicels of variable size. There is reason for thinking of these structures as labile. They may actually pinch off and contribute to the secretory product. In any case, the surface area is vastly increased by their presence. Polypoid border seems an apt term to apply to this type of surface.

3. There is also a great expansion of the basal surface of ependymal cells. In the vicinity of cell junctions this surface is deeply infolded, and continuous with elaborate interdigitations of the lateral intercellular surfaces. Analogous infolding of the basal cell surface is known to exist in other epithelia also noted for their water transport (kidney tubules, salivary gland, and ciliary body).

4. Pretreatment of rats with diamox, an agent known to block cerebro-spinal fluid production, did not produce an important morphological change in the features of the ependyma, or any other part of the choroid plexus.

5. Capillaries of the choroid plexus have a very attenuated endothelium. This is seen to be fenestrated. It is thought this probably represents the condition in life, and is not simply a fixation artefact.

6. Pial cells tend to interpose sheets of cytoplasm between the capillaries and ependyma. The sheets are not continuous, however, and so would not constitute a serious diffusion barrier. These cells belong to the reticuloendothelial system, and undergo shape changes, and probably increase in number, when the system is stimulated by the repeated injection of trypan blue.
POLARIZATION AND ELECTRON MICROSCOPE STUDY OF FROG NERVE AXOPLASM
Authors: Thornburg Wayne , De Robertis Eduardo
Published: May 2004

1. The submicroscopic organization of nerve axons from R. pipiens and R. catesbiana has been studied by means of polarizing and electron microscopes.

2. In measurements on a series of 85 fresh myelinated axons from which the sheaths had been removed average values were obtained for the total birefringence, +2.5 x 10–4, the form birefringence, +1.4 x 10–4, and the refractive index of the oriented component, 1.523. The average partial volume occupied by axially oriented filaments was computed to be 0.69 per cent.

3. Electron micrographs of fixed myelinated axons demonstrate an average of 93 axially oriented neuroprotofibrils per square micron of cross-section. The neuroprotofibrils are approximately 90 A in diameter, of indefinite length, and occupy a computed partial volume of 0.59 per cent.

4. Mitochondria, neuroprotofibrils, endoplasmic reticulum, and dense particles are seen in electron micrographs of both myelinated and unmyelinated nerve axons.

5. It is concluded that the neuroprotofibrils are present in the living nerve, that they play an important but undetermined role in nerve function, and that these structures are not an artifact of osmium tetroxide fixation.
CLOSE TOPOGRAPHICAL RELATIONSHIP BETWEEN MITOCHONDRIA AND ERGASTOPLASM OF LIVER CELLS IN A DEFINITE PHASE OF CELLULAR ACTIVITY
Authors: Bernhard W. , Rouiller C.
Published: May 2004

1. In most rat liver cells, no special topographical relationship between mitochondria and ergastoplasmic lamellae is to be observed. In some cells, nevertheless, the two organelles are grouped together in dense zones clearly separated from the hyaloplasm.

2. Such an association can be produced at will in the livers of animals refed after prolonged fasting, or in the regenerative phases after partial hepatectomy and intoxication with carbon tetrachloride. In all these cells, the ergastoplasm, after having disappeared, suddenly reappears in the cytoplasm, either along the nucleus or cell membranes, where the mitochondria are grouped.

3. It may be supposed that these topographical relationships between mitochondria and ergastoplasm during a definite period of cellular activity indicate a close functional link between chondrioma and basophilic structures. Mitochondria seem to play an important part in the elaboration of hepatic ergastoplasm.
QUANTITATIVE ESTIMATION OF LYO- AND DESMOENZYMES IN TISSUE SECTIONS WITH AND WITHOUT FIXATION
Authors: Nachlas Marvin M. , Prinn William , Seligman Arnold M.
Published: May 2004

1. Tissue sections eight microns thick were exposed to various experimental conditions used in histochemistry, and the effect upon the activities of esterase, the phosphatases, leucine aminopeptidase, ß-glucuronidase, and arylsulfatase was determined colorimetrically.

2. Significant differences were found in the amounts of the lyo and desmo fractions of these enzymes. The desmo components were found to be for esterase, alkaline phosphatase, leucine aminopeptidase, acid phosphatase, ß-glucuronidase, and arylsulfatase, ⅓, 2/3, 2/3, ½, ⅛, and ⅛ of the total enzymatic activity respectively.

3. Variations in the time and in the temperature at which diffusion was studied and of the pH and salt concentration of the solution into which the sections were placed, resulted in differences in the amount of enzymatic activity which remained in the tissue section. Some enzyme loss by diffusion was noted even after fixation of the tissue section.

4. The significance of the findings with respect to some of the concepts of localization of enzymes in tissue sections was discussed.
CONCENTRATION OF ACID PHOSPHATASE, RIBONUCLEASE, DESOXYRIBONUCLEASE, ß-GLUCURONIDASE, AND CATHEPSIN IN "DROPLETS" ISOLATED FROM THE KIDNEY CELLS OF NORMAL RATS
Authors: Straus Werner
Published: May 2004

1. Three fractions of "droplets" having diameters of 1 to 5 µ (fraction I), 0.5 to 1.5 µ (fraction II), and 0.1 to 1.0 µ (fraction III) were isolated from the kidney cells of normal rats.

2. All three "droplet" fractions showed 10 to 15 times higher activities of acid phosphatase, ß-glucuronidase, ribonuclease, desoxyribonuclease, and cathepsin than the total homogenate and the mitochondrial fraction.

3. After a rough fractionation of the total homogenate, approximately 50 per cent of the 5 enzymes was found in the fractions which contained the "droplets" and approximately 30 per cent in the supernatant fluid.

4. The similarities between the enzymatic properties of the "droplets" from kidney cells and of the fractions isolated from liver cells by other investigators have been discussed.
FACTORS AFFECTING THE PRODUCTION OF CHROMOSOME ABERRATIONS BY CHEMICALS
Authors: Kihlman B. A.
Published: May 2004

In the present paper, the results of a study on the influence of temperature, hydrogen ion concentration, and oxygen tension on the production of chromosome aberrations in Vicia root tips by maleic hydrazide (MH), di-(2, 3-epoxypropyl)ether (DEPE), and 8-ethoxycaffeine (EOC), are described.

Variations in the hydrogen ion concentration of the treatment solutions did not significantly influence the effect of EOC and DEPE. In contrast, the MH effect was considerably diminished by raising the pH from 4.7 to 7.3.

A marked increase in the frequencies of aberrations produced by DEPE and MH was obtained by raising the temperature from 3° to 25°C. The effect of EOC increased with rising temperature up to 12°C. With a further rise in temperature the effect of EOC decreased, so that at 25°C. it was of about the same magnitude as at 3°C.

The effect of EOC was completely inhibited, and that of MH partly so, when during the treatment (1) oxygen was excluded from the solution, (2) respiration was inhibited by azide or cyanide, or (3) phosphorylation was uncoupled from respiration by 2, 4-dinitrophenol (DNP). Pretreatments with DNP had a similar effect, but posttreatments did not influence the frequencies of aberrations. The effect of DEPE was unchanged by anoxia. Pre- or posttreatments with DNP did not change the total number of aberrations produced by DEPE, but the appearance of the effect was considerably delayed.

The results are discussed.
THE DISTRIBUTION OF NEWLY SYNTHESIZED DNA IN MITOTIC DIVISION
Authors: Plaut Walter , Mazia Daniel
Published: May 2004

The chromosomes of Crepis capillaris were labelled with thymidine-2-C14 in their DNA fraction. Quantitative analysis of the distribution of newly synthesized DNA in postmetaphase stages of the division following the period of label incorporation led to the conclusion that the new DNA is not necessarily equally distributed by the mitotic process and that, therefore, chromosome duplication does not involve the equal partition of parental DNA. The implications of these findings with respect to DNA duplication are discussed. An attempt is made to translate the pattern of new DNA distribution into a probable number of units of synthesis per chromosome.
THE NUTRITION OF ANIMAL TISSUES CULTIVATED IN VITRO
Authors: Morton Helen J. , Pasieka Arthur E. , Morgan Joseph F.
Published: May 2004

1. Cultivation of freshly explanted chick embryonic heart tissues in Hanks's salt solution for 3 to 4 days has been shown to create a general state of nutritional deficiency in the cultures. Provided the depletion is not prolonged beyond 4 days, the cultures subsequently revive and survive to a normal period in synthetic medium M 150.

2. Paper chromatographic studies on the culture medium have shown that the amino acid metabolism of the depleted cultures is restored to a normal pattern within a few days in medium M 150.

3. By the use of the nutritional deficiency technique, a coenzyme A requirement for this type of culture has been established.

4. The application of these findings to tissue cell nutrition and the possible hazards of using serum, or other uncharacterized additions, either to establish cultures, or as part of the experimental medium, are discussed.
PANCREATIC MICROSOMES
Authors: Palade G. E. , Siekevitz P.
Published: May 2004

The pancreatic exocrine cell of the guinea pig has a voluminous endoplasmic reticulum distinguished by extensive association with small, dense particles, and by its orderly disposition in the basal region of the cell.

In addition to the small, (∼15 mµ), dense particles attached to the limiting membrane of the endoplasmic reticulum, numerous particles of similar appearance are found freely scattered in the cytoplasmic matrix.

The various cell structures of pancreatic exocrine cells can be satisfactorily identified in pancreatic homogenates.

The microsome fraction consists primarily of spherical vesicles (80 to 300 mµ), limited by a thin membrane (7 mµ) which bears small (∼15 mµ) dense particles attached on its outer surface. The content of the microsomal vesicles is usually of high density. Pancreatic microsomes derive by extensive fragmentation mainly from the rough surfaced parts of the endoplasmic reticula of exocrine cells. A few damaged mitochondria and certain dense granules (∼150 mµ) originating probably from islet cells, contaminate the microsome fraction.

Pancreatic microsomes contain RNA, protein, and a relatively small amount of phospholipide and hemochromogen. They do not have DPNH-cytochrome c reductase activity. In six experiments the RNA/protein N ratios were found grouped around two different means, namely 0.6 and 1.3.

Pancreatic microsomes are more labile than liver microsomes but react in a similar way to RN-ase-(loss of the particulate component and RNA), and deoxycholate treatment (loss of the membranous component and of phospholipide, hemochromogen, and most of the protein).

Postmicrosomal fractions consisting primarly of small (∼15 mµ), dense particles of ribonucleoprotein (RNA/protein N ratio = 1 to 2) were obtained by further centrifugation of the microsomal supernatant.

The small nucleoprotein particles of these fractions are frequently found associated in chains or clusters.
THE EFFECT OF CORTISONE ON DNA CONTENT OF RAT HEPATOCYTES
Authors: Lowe Charles U. , Rand Royden N.
Published: May 2004

Rats were treated with cortisone, x-radiation, and both agents in combination, and the effect noted on the DNA content of hepatocytes. Nuclei were enumerated both in whole liver homogenates and following isolation. The incorporation of P32 into DNA was also studied in relation to these agents. The following observations were made:—

1.The DNA content of nuclei fell both during cortisone administration and following x-radiation. In the former instance, the fall was progressive with continuing administration of hormone; in the latter instance, there was a return to normal 5 days after radiation.

2. Cortisone administration to x-radiated rats caused a fall in DNA/nucleus and prevented the return to normal at 5 days.

3. There was no evidence that the effects of cortisone and x-rays were additive in reducing DNA/nucleus.

4. These data indicate an alteration in DNA/nucleus, but simple changes in ploidy cannot be excluded. Either explanation requires that the agents used affect the DNA of non-regenerating nuclei.

5. Cortisone interfered with the incorporation of P32 into the DNA of regenerating liver. Only a small effect on DNA synthesis in resting liver was observed with cortisone or x-radiation.

6. DNA content of nuclei returned to normal 5 days after x-radiation and 3 days after discontinuance of cortisone. Slight increase in the incorporation of P32 by DNA was observed during recovery phases.

7. The hypothesis is proposed that the apparent losses and increases in DNA/nucleus were due to depolymerization and repolymerization of DNA. Following x-radiation and/or cortisone administration, it is proposed that some DNA is depolymerized and becomes cold acid-soluble and dissociated from organized chromatin. Later, conditions are such that this degraded DNA is repolymerized.

8. These data might be interpreted to indicate that a portion of the DNA is not essential to cell integrity; alternatively, there may be two or more species of DNA, one of which is more readily affected by the agents investigated in the present report.
ELECTRON MICROSCOPE OBSERVATIONS ON INTRACELLULAR VIRUS-LIKE PARTICLES ASSOCIATED WITH THE CELLS OF THE LUCKÉ RENAL ADENOCARCINOMA
Authors: Fawcett Don W.
Published: May 2004

The common renal adenocarcinoma of the leopard frog was studied in thin sections with the electron microscope.

Approximately a third of the tumors examined were found to contain spheroidal bodies of uniform size and distinctive morphology that are believed to be virus particles. These consist of hollow spheres (90 to 100 mµ) having a thick capsule and a dense inner body (35 to 40 mµ) that is eccentrically placed within the central cavity (70 to 80 mµ). Virus particles of this kind occur principally in the cytoplasm but occasionally they are also found in the nucleus and in the extracellular spaces of the tumor.

The intranuclear inclusion bodies that are visible with the light microscope are largely comprised of hollow, spherical vesicles with thin limiting membranes. These are embedded in a finely granular matrix. A few of the thin walled vesicles contain a dense inner body like that of the cytoplasmic virus particles. This suggests that they may be immature virus particles. The inclusion bodies are believed to be formed in the course of virus multiplication but they usually contain very few mature virus particles.

Bundles of dense filaments and peculiar vacuolar inclusions also occur in the cytoplasm of the tumor cells. These seem to be related in some way to the presence of virus but their origin and significance remain obscure.

These findings are discussed in relation to previous work suggesting that the Lucké adenocarcinoma is caused by an organ-specific filtrable agent. It is concluded that the "virus particles" found in electron micrographs of the tumor cells may be the postulated tumor agent. On the other hand, the possibility remains that the particles described here are not those that are causally related to the tumors.
OOCYTE DIFFERENTIATION AND VITELLOGENESIS IN THE ROACH PERIPLANETA AMERICANA
Authors: Anderson Everett
Published: May 2004

The ovary of the roach Periplaneta americana has been studied by techniques of light and electron microscopy. Each ovariole (panoistic type) contains a linear array of oocytes in varying stages of development. Newly formed oocytes become encased by a layer of follicle cells and begin pinocytosis. All subsequent growth stages of the oocytes are dependent, in part, on this phenomenon. All of the pinocytotic caveolae show an unique surface modification; i.e., on their internal surface they have an amorphous or filamentous substance and their external surface is studded with many fine radially oriented spike-like projections. The pinosomes of early oocytes do not contain a demonstrable internal structure; they are thought to contain nutritive substances for the developing oocytes rather than yolk precursors. When the oocyte enters its last stage of growth, characterized by yolk deposition, the caveolae become filled with a dense material which is thought to be the precursors of yolk. Hence the conclusion is drawn that yolk formation is independent of any cytoplasmic organelle system of the oocyte and that the precursors of this deutoplasmic substance are manufactured outside the ovary and are internalized by the process of pinocytosis. Under the phase-contrast microscope the nucleoli of early oocytes are large irregular masses and show the phenomenon of nucleolar emission (fragmentation). These "emissions" become randomly dispersed in the nucleoplasm and some of them come to be intimately associated with the fenestrated nuclear envelope. After this process ceases, the main nucleolar mass becomes vacuolated. Electron micrographs suggest that the constituent particles of the nucleolar emissions migrate from the nucleus through patent pores of the nuclear envelope.
THE PROBLEM OF DEMINERALISATION IN THIN SECTIONS OF FULLY CALCIFIED BONE
Authors: Boothroyd B.
Published: May 2004

Thin sections of embryonic avian bone decalcify during preparation for electron microscopy, creating a false impression of mineral distribution. The results of the experiments reported herein show that viscous embedding materials do not penetrate compact formed bone, and so, in thin sections, the calcium apatite crystals may be leeched out by water, both in the collecting trough and in aqueous solutions of stains used to enhance tissue electron opacity. To prevent decalcification, a simple technique is described in which the aqueous fluids that come in contact with thin sections are saturated with respect to calcium and phosphate ions, thereby preventing solution of the bone mineral. The theoretical basis of this technique is briefly discussed.
THE RELATIONS BETWEEN DNA, RNA, AND PROTEIN IN NORMAL EMBRYONIC CELL NUCLEI AND SPONTANEOUS TUMOUR CELL NUCLEI
Authors: Seed John
Published: May 2004

Interferometric and photometric measurements have been made successively on individual cell nuclei derived from normal embryonic tissues and spontaneous tumour tissues of the mouse grown in vivo. From the measurements, the relations between nucleic acid and dry mass content have been studied in the two types of nuclei and the results shown to be consistent with differences in cell metabolism previously reported to exist in vitro. In the nuclei of normal embryonic cells, the syntheses of DNA, nuclear RNA, and protein appear to be closely associated, whereas in the tumour cell nuclei an appreciable fraction of the chromatin RNA and protein synthesis is dissociated from the replication of DNA.
ADIPOSE TISSUE
Authors: Williamson Joseph R.
Published: May 2004

Morphological changes associated with mobilization of lipid were studied in epididymal adipose tissue from fasted and from alloxan diabetic rats. In both groups of animals a decrease in lipid content was accompanied by the formation of complex frond-like cytoplasmic processes and of loops and folds of basement membrane which extended from cell surfaces. These changes, evident after 1 day of fasting, increased in magnitude with increasing weight loss. As the lipid content of the cell decreased further, lipid-cytoplasmic interfaces became irregular and convoluted. Cytoplasmic microvesicles were prominent and appeared to be greatly increased in number. Rosette-like structures composed of microvesicles were observed in both lipid-depleted fat cells and endothelium. The interpretation of these changes and their physiological significance are discussed in terms of the physical and chemical properties of lipids and lipid metabolism. It is postulated that microvesicles may represent the mechanism of transport of free fatty acids in fat cells and in endothelium. Hypotheses are proposed and illustrated schematically for the mode of formation of microvesicular rosettes, for the mobilization and uptake of lipids by fat cells, and for the transport of lipids through endothelium.
ELECTRON MICROSCOPY OF MITOSIS IN A RADIOSENSITIVE GIANT AMOEBA
Authors: Daniels E. W. , Roth L. E.
Published: May 2004

Various aspects of the ultrastructure of the dividing nuclei in the large radiosensitive amoeba Pelomyxa illinoisensis are demonstrated. Evidence of nuclear envelope breakdown is presented, and membrane fragments are traced throughout metaphase to envelope reconstruction in anaphase and telophase. Annuli in the nuclear envelope and its fragments are shown throughout mitosis. During metaphase and anaphase some 15 to 20 mitochondria are aligned at each end of the spindle, and are called polar mitochondria. The radioresistant amoebae Pelomyxa carolinensis and Amoeba proteus do not have polar mitochondria, and Pelomyxa illinoisensis is unique in this regard. The shape of the P. illinoisensis interphase nucleoli differs from that in the two radioresistant species, and certain aspects of nucleolar dissolution in the prophase vary. Helical coils in the interphase nucleoplasm are similar to those in the radioresistant amoebae. A "blister" phase in the flatly shaped telophase nuclei of P. illinoisensis is described which is interpreted to be the result of a rapid nuclear expansion leading to the formation of the normal spherical interphase nuclei.
THE DEGENERATION AND REAPPEARANCE OF MITOCHONDRIA IN THE EGG CELLS OF A PLANT
Authors: Bell Peter R. , Mühlethaler Kurt
Published: May 2004

Details are given of the elimination of mitochondria which occurs during the first 1 to 2 hours of the life of the egg of the fern Pteridium aquilinum (L.) Kuhn. During this phase the only mitochondria present are swollen and appear degenerate, but subsequently the cytoplasm of the egg becomes filled with large mitochondria containing numerous villi. Accompanying the appearance of these mitochondria, many, if not all of which have a peculiar umbo-like form, is the production by the nucleus of conspicuous and complex evaginations. The umbo-mitochondria are believed to be new, and a mechanism is suggested by which they may be generated from the complex evaginations of the nucleus.
OBSERVATIONS ON THE FINE STRUCTURE OF SPHEROPLASTS OF RHODOSPIRILLUM RUBRUM
Authors: Boatman E. S.
Published: May 2004

Spheroplasts of the photosynthetic bacterium Rhodospirillum rubrum were prepared from cultures grown in either the presence or absence of light. Cells were converted into spheroplasts by using lysozyme and Versene and fixed in a sucrose-veronal-acetate buffer mixture containing osmium tetroxide. Some preparations were shadow-cast and examined whole; others were embedded in Epon 812 and sectioned. The action of lysozyme and Versene appears to result in removal of the cell wall in strips. The relationship of the chromatophores to the cytoplasmic membrane is readily visualized in sections of broken spheroplasts, and in areas the chromatophores are seen to be continuous with the membrane. In all preparations examined, no definite connections between individual chromatophores were observed. In some cells large spherical granules were evident which either possessed or lacked a clearly visible limiting membrane. On serial sectioning, all granules appeared bounded by a single membrane 40 A wide. The granule membrane was well defined only if the section came from the center of the granule. Sections at other levels showed either a diffuse membrane or no membrane at all. The reasons for this are discussed.
YOLK PROTEIN UPTAKE IN THE OOCYTE OF THE MOSQUITO AEDES AEGYPTI. L
Authors: Roth Thomas F. , Porter Keith R.
Published: May 2004

Yolk proteins are thought to enter certain eggs by a process akin to micropinocytosis but the detailed mechanism has not been previously depicted. In this study the formation of protein yolk was investigated in the mosquito Aedes aegypti L. Ovaries were fixed in phosphate-buffered osmium tetroxide, for electron microscopy, before and at intervals after a meal of blood. The deposition of protein yolk in the oocyte was correlated with a 15-fold increase in 140 mµ pit-like depressions on the oocyte surface. These pits form by invagination of the oocyte cell membrane. They have a 20 mµ bristle coat on their convex cytoplasmic side. They also show a layer of protein on their concave extracellular side which we propose accumulates by selective adsorption from the extraoocyte space. The pits, by pinching off from the cell membrane become bristle-coated vesicles which carry the adsorbed protein into the oocyte. These vesicles lose the coat and then fuse to form small crystalline yolk droplets, which subsequently coalesce to form the large proteid yolk bodies of the mature oocyte. Preliminary radioautographs, and certain morphological features of the fat body, ovary, and midgut, suggest that the midgut is the principal site of yolk protein synthesis in the mosquito.
A CYTOCHEMICAL LOCALIZATION OF REDUCTIVE SITES IN A GRAM-POSITIVE BACTERIUM
Authors: van Iterson Woutera , Leene W.
Published: May 2004

In bacteria the exact location of a respiratory enzyme system comparable to that of the mitochondria of other cells has remained uncertain. On the one hand, the existence of particulate "bacterial mitochondria" has been advocated (Mudd); on the other hand, important enzymes of the respiratory chain were recovered in the cytoplasmic membranes associated with some granular material (Weibull). In order to gain insight into this question, sites of reducing activity were localized in thin sections of bacteria using the reduction of potassium tellurite as an indicator. When this salt was added to the culture medium of Bacillus subtilis, it turned out that in this Gram-positive organism the reduced product is strictly bound at two sites, and that the plasma membrane does not materially gain in electron opacity through deposition of the reduced product. The reduction product is found on or in the membranes of particular organelles, which may possibly be regarded as the mitochondrial equivalents in Gram-positive bacteria, and which are sometimes seen connected to the plasma membrane. The second location is in thin rod-like elements at the cell periphery, possibly the sites from which the flagella emerge.
LOCALIZATION OF CYTOPLASMIC NUCLEIC ACID DURING GROWTH AND ENCYSTMENT OF ENTAMOEBA INVADENS
Authors: Barker Douglas Cameron , Svihla George
Published: May 2004

With a modified color-translating ultraviolet microscope, the distribution of material showing an absorption maximum at 265 mµ was studied in samples from whole cultures of Entamoeba invadens at intervals during growth and from cysts allowed to mature under controlled conditions. Absorption by the cytoplasm in general gradually increased as trophozoites approached the period of maximum encystment. In late trophozoites and precystic forms, the absorbing material was concentrated into small bodies which coalesced to form large crystalloids of very high specific absorption. Maximum crystallization occurred in early cysts, where cytochemical tests have shown the large crystalloids to be ribonucleoprotein. Electron micrographs show that the crystalloids are composed of particles 200 to 300 A in diameter. During cyst maturation the amount of absorbing material per cyst is not visibly reduced, but the large bodies fragment into smaller units until finally there is only a very high diffuse absorption over the entire cyst. From these and other results the hypothesis is advanced that the large crystalloids ("chromatoid bodies") are a manifestation of a special parasite-host adaptive mechanism; ribonucleoprotein is synthesized under favorable conditions, crystallized in the resistant cyst stage, and dispersed in the newly excysted amebae thereby enabling them to establish themselves in a new host by a period of quick growth.
FINE STRUCTURE OF DIFFERENTIATING MOUSE PANCREATIC EXOCRINE CELLS IN TRANSFILTER CULTURE
Authors: Kallman Frances , Grobstein Clifford
Published: May 2004

Fine structural observations have been made in the 11-day embryonic mouse of exocrine cells in pancreatic epithelium developing in tissue culture transfilter from salivary gland mesenchyme of the 13-day embryonic mouse. After 2 days in culture, the exocrine cells show increased cytoplasmic density, abundant ribosomes in aggregate or "rosette" form, and expanded profiles of rough-surfaced endoplasmic reticulum. After 3 and 4 days in culture, the cells exhibit continued expansion of the profiles of endoplasmic reticulum, increased amounts of Golgi membranes, and large areas of light density (prozymogen granules). After 5 days in culture, dense zymogen granules are present in the most highly differentiated cells. In addition, at the filter-epithelial surface, at 2 days, small fibers can be discerned which, after 4 days in culture, show obvious periodicity and are thought to be collagen. The significance of these changes, in relation to the mesenchymal effect, to the onset of specific synthesis and to the stabilization of differentiation is discussed.
THE LOCATION OF ADENINE NUCLEOTIDE IN THE STRIATED MUSCLE OF THE TOAD
Authors: Hill D. K.
Published: May 2004

The location of tritiated adenine nucleotide was studied by autoradiography in toad muscle which had been fixed in an acetic acid/ethanol mixture, with lead acetate present to act as the nucleotide precipitant. The muscles were embedded in Araldite. The autoradiographs were examined in both the light microscope and the electron microscope. In confirmation of earlier work, it was found that at least 50 per cent of the adenine nucleotide is concentrated in the I band, near the A-I boundary, and evidence is now available to suggest that this fraction is located in the interfibrillar spaces rather than in the substance of the fibrils. Electron micrographs of unstained sections failed to show any structural features at the site in question, though the triads were made visible by the lead. However, when sections were stained with an alkaline solution containing lead, or with uranyl acetate, "vesicles" were revealed at the appropriate site and it is thought that these may be elements of a transverse network (reticulum) of tubules containing the adenine nucleotide. The location of phosphocreatine could not be investigated because this substance was lost from the muscle during the preparative procedure.
FINE STRUCTURE OF THE EYE OF A CHAETOGNATH
Authors: Eakin Richard M. , Westfall Jane A.
Published: May 2004

Electron microscopy reveals a star-like pigment cell at the center of the eye of the arrow-worm, Sagitta scrippsae. Between the arms of the pigment cell are clusters of photoreceptor cell processes, each process consisting of: (1) a tubular segment containing longitudinally arranged microtubules about 500 A in diameter and 20 µ in length; (2) a remarkable conical body, composed of cords and large granules, situated at the base of the tubular segment; and (3) a connecting piece which, like that of rods and cones, connects the process with the sensory cell proper and through which runs a fibrillar apparatus consisting of nine peripheral double tubules. Beneath the connecting piece lies a typical centriole with a striated rootlet. The receptor cell process is deeply recessed into the sensory cell which may possess a corona of microvilli at its inner surface. A nerve fiber arises from the outer end of the cell and passes into the optic nerve. Additional features are some supporting cells, an external layer of flattened epithelial cells, and an over-all investment of basement membrane and thick fibrous capsule. The fine structure and function of these elements of the eye are discussed in relation to earlier studies with the light microscope. The ciliary nature of the photoreceptor cell process in S. scrippsae points to a probable evolutionary relationship of chaetognaths to echinoderms and chordates.
ASSEMBLY AND AGGREGATION OF TOBACCO MOSAIC VIRUS IN TOMATO LEAFLETS
Authors: Shalla Thomas A.
Published: May 2004

Cells of tomato leaflets (Lycopersicum esculentum Mill.) were studied by phase and electron microscopy at various intervals after inoculation with a common strain of tobacco mosaic virus (TMV). Forty-eight hours after inoculation, prior to the development of assayable virus, individual TMV particles, and also particle aggregates, were observed in the ground cytoplasm of mesophyll cells. The most rapid synthesis of virus occurred between 80 and 300 hours after inoculation. Cytological changes during this time were characterized by an increased number of individual particles in the cytoplasm, growth of some aggregates, distortion and vacuolation of chloroplasts, and formation of filaments in the cytoplasm which were approximately four times the size of TMV. These filaments were interpreted as possible developmental forms of the TMV particle. Vacuoles in chloroplasts commonly contained virus particles. Evidence indicated that TMV was assembled in the ground cytoplasm and, in some cases, subsequently was enveloped by distorted chloroplasts.
CELL DIVISION AND DNA SYNTHESIS IN TETRAHYMENA PYRIFORMIS DEPRIVED OF ESSENTIAL AMINO ACIDS
Authors: Stone G. E. , Prescott D. M.
Published: May 2004

The question of amino acid requirements for DNA synthesis and cell division has been studied in Tetrahymena pyriformis by depriving cells of histidine and tryptophan at defined stages in the interdivision interval. Deprivation any time before DNA synthesis does not prevent the initiation of such synthesis but completely inhibits the following division and limits the increase in DNA, as measured microspectrophotometrically, to 20 per cent. H3-thymidine added to the medium is not incorporated during the 20 per cent increase. Deprivation after DNA synthesis is initiated does not prevent the continuation (to completion) of DNA synthesis, and cell division ensues. H3-thymidine added to the medium under these conditions is incorporated into macronuclear DNA. The data indicate that some amino acid-dependent event occurs, about the time of the beginning of the DNA synthesis period, which is not essential for initiation of DNA synthesis but which is essential for the maintenance of synthesis once it has begun. These results are further discussed in terms of enzymes required to convert thymidine (and possibly the other three deoxyribonucleosides) to the immediate precursor of DNA synthesis.