90 BIOLOGICAL & CHEMICAL ASPECTS OF SOME ANIMAL NEOPLASMS [Vol. XXI, Part II,
research proved to be of less value than was anticipated, Greene claims that intra-
ocular heterologous transplantation is a test for malignancy and degree of autonomy
of tumors. It has also been claimed that all tumors which possess the ability to
invade and metastasize can be successfully transplanted to alien species and that
the completely disorganized tumors often undergo alternations to reveal organized
structure indicating the tissue or organ of origin in cases in which this was obscure
in the primary host [Greene, 1948; Schilling, Snell and Favata, 1949].
Straus and Cheronis [1948] are of the opinion that tumor cells in contrast to
normal mammalian cells obtain energy from glycolysis even in the presence of
oxygen and if this difference in the amount of glycolysis in the neoplastic cell is
present to an appreciable extent it might be demonstrated by reagents which are
capable of reacting with enzymes. They observed that carcinomatous tissues
when immersed in one per cent aqueous solution of triphenyl tetrazolium
chloride developed pink colour within thirty minutes owing to the reduction of
tetrazolium into formazan by the enzyme present in the neoplasm. The uninvolved
surrounding tissues remained unstained even after six hours of immersion.
One
hundred and sixty-four animal neoplasms were studied in regard to their chemical,
morphological and biological aspects. One hundred and eighteen were melanomas
(one hundred and eight from horses, eight from dogs, and two from swine), forty-
two carcinomas and four connective tissue tumors. Representative pieces from
melanotic tumors were used to prepare frozen sections stained by dopa reagent and
paraffin sections by protogol and gold chloride stain of Bodian. These stains which
were specific for melanoblasts were used as controls to compare the reaction in
paraffin sections stained by Acetic-Fuchsin-Formalin method of Castroviejo.
Highly pigmented tissues were bleached by immersing in three per cent hydrogen
peroxide for six days prior to staining.
The dopa-positive and silver protein-positive melanoblasts were found to be
fuchsin-positive in paraffin sections of melanomas. Therefore modified Castroviejo's
stain is regarded as a convenient method to identify a true melanotic tumor with
routinely prepared paraffin sections from fixed tissues. Melanophores, experi-
mentally produced by injecting melanin suspension into albino rabbits were
negative to fuchsin when subjected to Castroviejo's stain. The stain provides easy
means of differentiation between a true melanin-producing cell and a phagocytic
cell containing melanin and it seems to be a reliable test especially for the identifica-
tion of amelanotic melanomas in paraffin sections.
Cytological features and histological appearances were not similar in all
melanomas studied. Variations in size, shape and pattern of arrangement of
melanoblasts were observed. They were either oval or polyhedral in shape usually
with a single nucleus but rarely multinucleated. Melanoblasts were arranged in
parallel cords or in acinar groups or presented in indefinite pattern. Structures
resembling Wagner-Meissner's corpuscle were observed in some cutaneous melanomas.
Melanotic pineal bodies of horses and a few melanomas of muscles and salivary
glands showed dendritic melanoblasts. Melanomas of gray horses were infiltrative
and highly anaplastic and regarded as malignant not only by the morphological
appearance but also by their ability to grow in the anterior chamber of guinea pig
eyes. The pigment-producing function of melanoblasts was not impaired by their
residence in the anterior chamber.