658 II. M. WOODCOCK. 



vvliicli it would be tedious to cite in detail (cf. the remarks 

 by the Sergents [29], Novy and McNeal [14], Laverun [6], 

 Button and Todd [4] , and others). I will only add that Petrie, 

 ill the note already referred to, states that he could not find 

 the trypanosomes in the blood of any of the infected birds, 

 l>nt only saw them in the bone-marrow. With respect to this 

 numerical scarcity, birds are certainly the most trying of all 

 vertebrate hosts. There can be no doubt that, owing to this 

 factor, an erroneous idea has often been obtained of the pre- 

 valence of trypanosome infectious among birds. This has 

 been well shown by Novy and McNeal, whose adoption of 

 the culture method is of very great value in this connection. 

 It will sufficiently illustrate this to give the statement of 

 these authors that, in the case of forty-three various birds 

 where microscopic examination had failed to reveal try- 

 panosomes, nineteen, or 44 per cent., were proved by means 

 of cultures to have been infected. 



To give now my particular experiences. Out of five 

 naturally infected chaffinches only in one were trypanosomes 

 ever seen in freshly drawn peripheral blood ; in this case, I 

 once saw an individual in a cover-slip preparation. The 

 same bird was examined at intervals during three months 

 subsequently, but I never saw any living parasites again. 

 That they were still present in the general circulation, how- 

 ever rare, was proved nevertheless on three occasions by 

 means of cultures. Once, determined to find this elusive 

 parasite if possible, I took a few drops of blood and made 

 several smears, which were fixed and stained. In six good- 

 sized films, which were minutely and thoroughly searched, 

 representing a labour of several days, only one trypanosome 

 was seen ! It is important to note that these observations 

 were made during the early spring, from January to April. 

 In the case of the trypanosome parasitic in the redpoll I was 



This writer was in the liappy position of being able to say that the 

 parasites were not infrequent in the peripheral circulation. An indivi- 

 dual could be found in every two or three fields (of an oil-immersion 

 lens). 



