THE PATHOGENIC PROTOZOA 147 



rendered so famous by Pasteur. Under the microscope the 

 presence of the germ was demonstrated in the egg, and it was 

 recognized that the infected eggs produced caterpillars which 

 formed the point of departure for the infection of the following 

 year. In general,**in this example the heredity is only of one 

 generation, for the silk-worm infected in the egg rarely survives 

 to become an adult ; it is the other silk-worms, infected late in 

 their larval stage, which succeed in reaching the adult con- 

 dition after more or less great vicissitudes, which produce the 

 infected eggs. 



Eckhardt has found coccidia (Cocddium tenellum) in the 

 white of hen's eggs, and, according to him, these parasites 

 produce an early infection of the chicks which in consequence 

 very soon die. 



The higher vertebrates have an interest in the hereditary 

 transmission of protozoal diseases from two points of view ; 

 either it occurs in themselves or it is a condition of the 

 infection of an invertebrate host which transmits to them the 

 disease. Thus the piroplasmosis due to Piroplasma bigeminum 

 is transmitted from ox to ox by a tick, Rhipicephalus annulatus, 

 but it is not the same individual tick which carries the 

 piroplasma from one ox to another. One tick becomes 

 infected from an infected ox, and it is its progeny, a daughter 

 tick, which infects the healthy animal. On the inheritance of 



the parasite in 

 the insect-carrier 

 depends the pro- 

 pagation of the 

 disease in the 

 vertebrate. 



FIG. 58. The spirochaete of syphilis : forms in An mh entance 

 longitudinal division. IS probable also in 



other diseases of 



vertebrates which are transmitted by ticks, e.g., the spirillosis of 

 fowls, African tick-fever and recurrent fever. R. Koch saw the 

 spirochaete of African recurrent fever in the egg of the 

 tick which transmits it, Ornithodorus moubata. In fowls 



L 2 



