is, 4 Haughwout: Human Coccidiosis 463 
The stool passed on March 15, which was light yellowish 
brown and soft-formed — much softer than the other — was exam- 
ined on April 1, after it had rested under similar conditions. It 
contained a number of healthy-appearing cysts in full develop- 
ment, but with shrunken oocysts, and also large numbers of 
cysts in various stages of development up to full development, 
which had undergone marked degeneration in addition to the 
wrinkling of the oocyst. Contraction or wrinkling of the oocyst 
does not, however, necessarily mean that the cyst is not infective, 
as I shall try to show later. Death of the protoplasm is prob- 
ably quickly followed by its disintegration, even under the double 
protection afforded by the oocyst and the sporocyst. 
The proportion of cysts discharged from the intestinal mucosa 
that fail to develop for one reason or another, is probably rather 
large, and I am at present trying to determine that approxim- 
ately, but it will take the consideration of many cases to give 
any definite idea. It would seem to me to be a much larger 
proportion than is the case with the cysts of Entamoeba histo- 
lytica. From time to time, one encounters cases of infection with 
the latter organism in which the greater number of the cysts 
examined are in the mono- or binucleate stage. As Dobell (4) 
has pointed out (p. 48), and as my own experience corroborates, 
these cysts undergo no further development after they have 
left the intestine. I am inclined to believe that they hail from 
nests of amoebas located in the tissues lying rather low down 
in the intestine, whence the journey to the outer world is too 
short to give them time for full development. These cases are 
relatively uncommon, and it is likely that such cysts are incapable 
of infecting a new host. 
So far as my observations have led me, I am inclined to 
believe that there are three general causes underlying the fail- 
ure of these cysts of Isospora to develop: (1) failure of the 
macrogamete to be fertilized by a microgamete, (2) failure of 
the macrogamete to store sufficient energy in the form of food 
reserve to carry if through the rather dynamic processes of divi- 
sion and differentiation which, from the behavior of the zygote 
during the earlier stages of sporogony, would seem to call for 
the expenditure of not a little energy, and (3) a variety of 
untoward environmental conditions. 
Four undeveloped and more or less degenerate cysts are shown 
(Plate 3, figs. 1, 3, 4, and 11). Fig. 1 shows a cyst, the pro- 
toplasm of which, it is true, is somewhat vacuolated, but perhaps 
not unduly so, although I have not sufficient knowledge of the 
