STUDIES ON AVIAN H.EMO PROTOZOA. . 647 



above as a reliable test of the presence of the trypanosomes 

 in the living bifd. 



Culture Media. — The parasite from the chaflEinch and 

 redpoll lives and multiplies readily in a blood-agar medium, 

 prepared either after Novy and McNeal's recipe, or according 

 to Mathis' modification. At first I followed the American 

 authors (see 14, p. 265), but added only an equal volume 

 of defibrinated i-abbit's blood to the sterilised meat-agar, 

 as I found this to be quite sufficient. Tubes so prepared 

 always have an ainple quantity of expression-liquid, in which 

 the parasites thrive at any temperature from 20° to 25° C. A 

 temperature of 28° to 30° C. was found to be too high, if it 

 was desired to keep the tube for any length of time, as the 

 trypanosomes soon die off, owing to their too rapid multiplica- 

 tion and exhaustion of the nutrient material. At the lower 

 temperature the tube is all right for about twelve or fourteen 

 days, and some of the trypanosomes will remain alive longer 

 if a little salt-citrate solution is added to replenish the 

 medium. If it is desired to keep the culture going for some 

 time, however, it is necessary to make a sub-culture, after 

 ten or twelve days, by transferring a drop of the medium 

 containing the parasites to a fresh tube. By this means I 

 have kept a continuous series of cultural forms, both from 

 the chafiinch and from the redpoll, thriving and multiplying 

 for six and a half weeks, the one having been transferred 

 (sub-cultured) four times, the other, I think, only thrice. 

 Had it not been for the accident of the temperature of the 

 incubator rising to nearly 30° 0. for two or three days, 

 whereby the trypanosomes were all killed off, the cultures 

 could apparently have been kept for as long as I wished. 



The great drawback to this method is that, where, as in my 

 case, a lai'ge number of the tubes are used, too much time 

 and labour are involved in obtaining sufficient rabbit's blood. 

 Mathis' modification (10), which I have now followed for 

 some time, avoids this difficulty. In this method, ox-blood, 

 which can be readily got from a slaughter-house, is used 

 instead. A quantity is allowed to fall direct into a sterilised 



