TRYPANOSOMES 69 



of the parasites in the intermediate (invertebrate) hosts was investigated, and 

 allied species were obtained from many different hosts. 



Novy and MacNeal (1903) were the first to cultivate trypanosomes in artificial 

 media (blood-agar). 



In 1910 Stephens and Fantham recorded the presence of another human 

 trypanosome, T. rhodesiense, from a case of sleeping sickness in Rhodesia, where 

 G. palpalis was absent. Kinghorn has since demonstrated that T. rhodesiense is 

 transmitted by G. morsitans. Kinghorn and Yorke believe that big game (e.g., 

 antelope) is the reservoir of T. rhodesiense. 



The output of literature on trypanosomiasis in men and animals is enormous. 

 To cope with it the Sleeping Sickness Bureau Bulletin was founded in 1908, 

 and it is now (since November 1912) continued as a section of the Tropical Diseases 

 Bulletin, wherein current literature is reviewed. 



GENERAL. 



Trypanosomes occur in the blood of representatives of all the 

 vertebrate classes. Often the trypanosomes occur so scantily in the 

 blood that they are overlooked on examination. A useful aid in 

 detecting the flagellates in such cases consists in the use of cultures 

 of the blood of the host on artificial media. Stimulated by the 

 medium multiplication occurs, and hence the parasites are more 

 easily detected. [For the composition of such culture media see 

 Appendix.] 



There is a periodicity in the appearance of the trypanosomes in 

 the peripheral blood of the host, due to alternating phases of multi- 

 plication and of rest on the part of the parasites. Such periodicity 

 has been established both by biological and enumerative methods. 

 Again, a seasonal variation has been observed in the occurrence 

 of certain trypanosomes in the peripheral circulation of the hosts ; for 

 example, some trypanosomes (e.g., T. noctuce in birds) are found only 

 in the summer in the blood, while in the winter they occur in the 

 internal organs. 



Recent cultural researches have established that trypanosomes, e.g., 

 T. americanum, may be present in very small numbers in hosts, such as 

 cattle, which are quite unharmed by them, and in which the presence 

 of these flagellates formerly was never suspected (" cryptic trypano- 

 somiasis.") However, the majority of the trypanosomes occurring in 

 domestic animals are usually deleterious or even lethal to their hosts. 

 Many wild animals, such as various species of antelope, harbour 

 trypanosomes without being injured thereby. In such cases it is 

 probable that the vertebrate hosts have been so long parasitized in the 

 past, that they have become tolerant and immune to the effects of the 

 flagellates. Should such trypanosomes of wild animals be transmitted 

 to domesticated stock or man, they may re-acquire their initial viru- 

 lence and become pathogenic to the new host. As a general state- 

 ment, the newer a parasite is to its host the greater is its virulence. 



