48 PRACTICAL PARASITOLOGY 



between the tenth and fourteenth days. They are considerably more 

 slender than the flagellate forms cultivated upon a citrate of soda 

 medium by Kinoshita, and for this reason approximate more closely 

 to the Leishmania donovani type. They differ from it, however, in 

 the possession of an undulating membrane which completes their 

 resemblance to the Trypanosomes. They multiply, in the same way 

 as other Flagellates, by longitudinal fission. At room temperature 

 they remain active for forty-five days ; at a temperature of 10 to 

 20 C., up to three months. As with Novy's method, secondary 

 cultures may be made by inoculating fresh blood-bouillon with 

 material taken from the first culture. It was found possible to infect 

 a calf with Babesia by inoculation with pure culture parasites. 



(4) TRANSMISSION BY BLOOD-SUCKING ANIMALS. 



There is no doubt that, with but few exceptions (as Trypanosoma 

 equiperdum, which is transmitted by coition), blood parasites are 

 transmitted by means of blood-sucking animals, although with many 

 species the exact manner in which this takes place is not known. 

 Two different types of infection are, however, distinguished. 



(1) A true change of host, the blood-sucking animal being the 

 host of the parasite, which can only be transmitted to a second or 

 intermediate host after the completion of a certain stage in the 

 development of the parasite. An instance is afforded by the convey- 

 ance of the malaria parasite from the mosquito to man. 



(2) A mechanical infection, by the agency of a blood-sucking 

 animal in which the parasite does not undergo further development 

 and which is, therefore, not its true host, but which is, nevertheless, 

 able to convey infection when its sucking or intestinal apparatus 

 retains traces of infective material with which it has come into recent 

 contact. Thus, Spiroschaudinnia recurrentis, the organism of 

 relapsing fever, is carried by bed-bugs and rat-lice. It would appear 

 from recent experiments that the Trypanosome of sleeping sickness 

 is conveyed to man by Glossina palpalis, its true host being probably 

 G.fusca. 1 



All blood-sucking invertebrates convey blood parasites, or are, at 

 the least, seriously suspected of so doing. The following groups have 

 come within the author's somewhat limited experience. 



Mosquitoes and gnats are the true hosts of a large number of blood 



1 See E. A. Minchin. " Investigations on the Development of Trypanosomes in 

 the Tsetse-flies and other Diptera," Quarterly Journal of Microscopical Science, 

 vol. lii, 1908, pp. 159-260. 



