86 The Philip-pine Journal of Science ms 



solutions of potassium bichromate, which will arrest putre- 

 factive changes that tend to bring about abnormal development 

 of the cysts. 



From the foregoing it will be seen that the disposal of matter 

 containing coccidial cysts may prove to be a very troublesome 

 problem. Quicklime seems to exert the most destructive action 

 on these cysts of any of the disinfectants in common use. 



Cysts of species of the genus Coccidium are frequently passed 

 in a stage of advanced development, so that they may become 

 infective very soon after they leave the intestinal tract of the 

 original host. But development to the sporozoite stage in the 

 case of Isospora does not, as a rule, become complete until two 

 or three days have elapsed after the cysts have left the host. It 

 should be understood that the sporozoites are the end product 

 of sporogony, and they are the form in which the parasite enters 

 the epithelium of the new host. If a cyst in a developmental 

 stage preceding sporozoite formation is taken into the alimen- 

 tary tract of a new host, the cyst envelope is dissolved and an 

 inert mass of protoplasm is liberated that is incapable of doing 

 harm and that probably very quickly disintegrates. 



Notwithstanding the immense amount of work that has 

 been done on this group of the Protozoa, apparently very little 

 has been done on the specificity of these parasites to partic- 

 ular hosts. Coccidium cuniculi is generally credited with being 

 infective to rabbits, dogs, cattle, and man, it being suggested 

 that man may become infected through eating livers of rabbits 

 containing the sporocysts of the coccidium. This theory seems 

 to me to be untenable. In the first place the cysts seem to be 

 unable to complete their development in the liver and in many 

 cases eventually degenerate. Furthermore the presence of car- 

 bon dioxide in the liver apparently exerts an exceedingly dele- 

 terious effect upon them, resulting finally in their destruction, (l) 

 Such a condition is frequently found in old rabbits that 

 have spontaneously recovered from an earlier coccidial infec- 

 tion. But even allowing that these causes may not always 

 be operative, it seems to me hardly likely that the cysts will 

 retain their vitality through the process of cooking, even though 

 they be walled off from the general mass of the liver by con- 

 nective tissue capsules. A method of infection similar to that 

 obtaining in the case of Entamoeba histolytica or other protozoa 

 or helminths of similar habitat seems to me much more likely. 



On the other hand, on contrasting the two almost similar 

 species, Coccidium avium of birds and Coccidium cuniculi of the 

 rabbit, it is seen that the rabbit coccidium will not infect birds 



