March 1955]
H.
N.
RAY
AND
B.
S.
GILL
21
nature of plasmagene which in collaboration with K, killer factor in nucleus,
confers upon its possessor the facility of secreting a poisonous substance which kills
individuals of sensitive race [Sonneborn, 1939]. Lwoff [1952] also described Feulgen
positive particles, the provirus particles, in certain lysogenic bacteria. The present
investigations adds another example showing the occurrence of extra nuclear DNA.
Oocysts showing DNA in them and those devoid of it are all seen at the same stage
of maturity. This rules out the possibility that DNA might be developing in all
oocysts at a certain stage. Further, it may be said that the oocysts devoid of DNA
which occur in solid majority may be abnormal ones ; but this is contrary to the
experience that a majority of oocysts voided in faeces develop normally and are
viable. It may also be argued that these oocysts which possess DNA and occur in
minority may not be normal ones, but the ordinary cytological and histological
methods of staining fail to detect any differences in their structure which could
lead one to believe that there occurs a proportion of oocysts which are abnormal.
Moreover, there seems to be no plausible reason to believe that the possession of
DNA by them will be derogatory to their survivability. It may also be argued that
these cytoplasmic DNA particles may be elements of viral nature or may be bacteria
which have gained access to the developing macrogametes or oocysts. But, this
analogy with bacteria or virus is by no means perfect. It is probably safe to regard
that these particles have a peculiarity of their own and their precise role in the
organism yet remains to be understood. However, it should be admitted that DNA
is rarely found outside chromosomes, and we may, therefore, be dealing with a
phenomenon of limited occurrence. Therefore, it is concluded that there are actually
two types of oocysts in the experimental infections due to a ' pure' line strain of
E. tenella which behave differentially with regard to the distribution of nucleic acids
in them. A large number of sporozoites studied, both in the lumen and just entered
epethelial cells, show a moderate quantity of low polymer of DNA in their nuclei.
The facts that all the sporozoites possess DNA, and a solid majority of oocysts do
not contain DNA at all, are not reconcilable with each other. These findings of
E. tenella drag the discussion to an already hotly disputed subject of the conver-
sion of RNA into DNA—a view elaborated by Brachet [1950] who has devoted
considerable space in support of his arguments and to which the reader is referred.
But one fact is clear that the majority of oocysts as they leave the parasitised caecal
pouch are devoid of any detectable quantity of DNA in them. Thus, the DNA
of sporozoites formed from such oocysts must have been formed de novo during the
process of sporulation. Evidence is available on the de novo synthesis of DNA in
ciliates [Seshachar, 1950] spectrophotometrically, and Seshachar and Dass, [1953b]
cytochemically, where de novo synthesis of DNA in Chilodonella and Epistylis arti-
culta respectively have been demonstrated. This investigation on E. tenella fur-
nishes a proof, though an indirect one, of the de novo synthesis of DNA in this
coccidium.
SUMMARY
Distribution of nucleic acids in E. tenella has been described in detail at its
various endogenous stages. An attempt has been made to correlate these findings
with the biological tempo of the parasite. It was interesting to note that macro-
gametes were devoid of any detectable DNA, while only a small minority (about