June, 1955]
B.
S.
GILL
81
The regimen of thiouracil and thyroprotein feeding followed in these experi-
ments had induced sufficient degree of hypo- and hyperthyroidism as indicated by
change in size, weight and histology of thyroids.
Thyroids of the thiouracil-fed group were almost 10 times enlarged than thyroids
of the unmedicated group. Histologically, marked hypertrophy and hyperplasia
of the columnar cells and complete absence of colloid from the lumen of acini and
acute distension of blood vessels were seen. These macro- and microscopic changes
are clear evidence of the effectiveness of thiouracil treatment. Thyroids of the
' protamone '-fed group were atrophied. This diminished thyroid size was similar
to that reported by Irwin, Turner and Reineke [1943]; Turner, Irwin and Reineke
[1944], and Wheeler et al., [1948]. Acini were almost replaced by fibrous tissue.
Thyroids were considerably decreased in size and could be located and dissected
out with difficulty. They had less than half the weights of thyroids of control
groups. Acute atrophic picture of thyroids established the effectiveness of the
thyroprotein treatment.
Oocyst production
Each group showed peak of oocyst production at the end of the 7th day of infec-
tion after which a marked reduction in the oocyst population in faeces was noticed.
This fact is in line with our knowledge of life cycle of the parasite in that the gamete
stage is reached on the 6th day when fertilisation takes place, and a great majority
of oocysts are eliminated on the 7th to 9th day. Later elimination of oocyst is
kept up by the progeny of ' lag-phase '.
Oocysts being the direct filial descendants of preceding stages, and the only
stage in the life history of the parasite lending to numerical counts, can indicate
with all its limitations, the growth rate of the parasite. Any factor influencing its
growth, which is necessarily through schizogonous cycle, which incidentally is also
the vulnerable stage inside the host, will be reflected in the quantitative change it
has affected in the oocyst discharge. Therefore, counting of oocysts was relied
upon to compare the overall growth rate of the parasite in the normal, hypo- and
hyperthyroid hosts. Other standards., viz. haemotologic count and haemolglobin
determination used by various authors indicate changes which are only manifesta-
tions of the acute disease set up by massive doses. A single dose of 250 oocysts
used in this experiment could produce only a mild infection, hence, these standards
were not taken into consideration.
The thiouracil-fed group produced the least number of oocysts. The control
group produced 2.9 per cent more oocysts than the former lot. This difference is
probably not a significant one, whereas the ' protamone '-fed group has produced
a significantly more number of oocysts, viz. 501 and 489 per cent more than the
hypothyroid and normal chicks respectively. The observation of Todd et al.,
[1949] that hyperthyroid chicks produced 11 times more oocysts than the control
is similar to the present investigation but as their observation was made on the
23rd day of infection, and was not a count of the total oocyst production, the two
observations cannot be fully compared.
From the data presented, it is evident that moderately elevated B. M. R. of
host chicks has favoured growth of the parasite, as is shown by the higher rate of