50 PRACTICAL PABASITOLOGY 



Patton, the kala-azar parasite, Leishmania donovani, is conveyed 

 by Acanthia rotundata. 1 



Ticks are important as being the vehicle by which Babesia are 

 conveyed. In Germany, Babesia bovis is conveyed to cattle by Ixodes 

 ricinus. Ticks are particularly interesting as being the transmitters 

 of Hsemogregarines, experiment having proved I. ricinus to be the 

 true host of Carolysus lacertarum. Many forms of Spirochgeta in- 

 fection are conveyed by ticks. Such are the African tick-fever of man, 

 caused by Spiroschaudinnia duttoni, and those forms of Spirochseta 

 infection which have been artificially induced in cocks and hens. 



Leeches undoubtedly convey blood parasites to tortoises, amphibians 

 and fishes, although definite information as to the actual species 

 transmitted is w r anting. 



When experimentally inducing a parasitic infection of the blood, 

 it is before all things necessary to ascertain by repeated blood tests 

 that the animal to be experimented upon is free from all previous 

 taint. Theoretically, the blood-sucking animal by means of which 

 parasites are to be conveyed from the infected vertebrate to a fresh 

 host, should also be examined. In practice, however, this is not 

 possible, as in the greater number of cases the requisite proof could 

 only be furnished by the section and microscopic examination of the 

 body of the intermediate host. Such would be the case, for instance, 

 with a mosquito containing malaria parasites. Attempts have been 

 made to overcome this difficulty by using invertebrates which have 

 been cultivated from the egg, or at least from the larval stage, in the 

 laboratory. But the method is successful in certain cases only (as, 

 for instance, mosquitoes which are to be infected with Proteosoma, or 

 the parasites of human malaria), as many blood parasites are trans- 

 mitted to the eggs of their host and infection is thus congenital. 

 Such is the case with Babesia in ticks, Hcemoproteus noctuce in 

 Culex, and Hcemogregarina stepanowi in Placobdella. Speaking 

 generally, the most that one can do is to employ as many subjects 

 for experiment as possible ; to follow the development of the parasites 

 in the body of the blood-sucking host ; and to guard against error by 

 careful observation of control subjects. Every now and then it may 

 be possible to procure animals for experiment from districts where the 

 particular Protozoon under observation is either absent or very rare. 



We shall now give minute instructions for the microscopic ex- 



1 W. S. Patton, "Preliminary Beporfc on the Development of the Leishman- 

 Donovan Body in the Bed-bug," " Scient. Mem. by Off. of the Med. and Sanit. Dep. 

 of the Governm. of India," No. 27, Calcutta, 1907, 4to, p. 19. W. S. Patton, " The 

 Development of the Leishman-Donovan Parasite in Cimex rotundatus^ Second 

 Eeport, ibid, No. 31. Calcutta, 1907, 4to, p. 26. 



