4 TROPICAL MEDICINE AND HYGIENE 



flagellata and the sporozoa is not a sound one, as flagel- 

 lates have a quiescent stage when they resemble sporozoa. 

 Much more work is necessary in connection with the 

 protozoa and their sexual cycles and transformations 

 before we can safely alter the present usual classification, 

 and any premature attempts at regrouping these organisms 

 are to be deprecated. 



Development and Life-history. This is not known in all 

 the genera, but where it is fully known two methods of 

 multiplication can be shown to occur asexual or vegeta- 

 tive, and sexual. As a type of the life-history and method 

 of reproduction of the sporozoa that of coccidia may be 

 taken as an example. The analogies with the develop- 

 ment of the malaria parasites will be considered with 

 them. 



In the coccidia, entrance to the warm-blooded host 

 is gained through the alimentary canal. The young 

 coccidia spores, sporozoltes, are set free from the cyst in 

 which they are contained by the action of the digestive 

 juices and penetrate into the epithelial cells of the 

 intestinal mucosa, or of one of the appendages of the 

 intestine such as the bile passages and the liver. 



When the young coccidia have entered such a cell 

 they grow until they have entirely filled and destroyed it. 

 Division of the protoplasm of the coccidium now takes 

 place. The outer part of this has formed a cyst wall, and 

 thus a cyst is formed containing a large number of young 

 coccidia or spores. The cyst wall then ruptures, the 

 young coccidia are liberated and pass into other intes- 

 tinal or hepatic cells. The process is repeated over and 

 over again, and massive tumours are thus formed by the 

 coccidia which have multiplied asexually. Coccidia which 

 develop into asexual forms are known as "schizonts." 

 Some of the spores of young coccidia develop in a dif- 

 ferent manner. No division of the cell contents takes 

 place, but the protoplasm remains undivided with a 

 single nucleus. A weak spot in the cyst wall, known 

 as the micropyle, is present. Such forms are the female 



