46 PRACTICAL PABASITOLOGY 



should be inoculated four weeks before it is proposed to examine 

 them. Sometimes, though not always, the resulting infection may 

 be only slight, and for this reason the blood should be tested daily 

 between the tenth and twentieth days. If the parasites begin to 

 decrease in numbers, two fresh canaries should be inoculated with 

 the blood of the first two. By this method Proteosoma may always 

 be obtained in large numbers. 



Of the Babesia, Babesia canis is the most favourable for examina- 

 tion purposes. Inoculation should be subcutaneous and a large 

 quantity (15 to 20 c.cm.) of material should be used. 



(3) CULTIVATION OUTSIDE THE BODY. 



A certain number of blood parasites may be cultivated upon sterile 

 media outside the body of their host. By taking suitable precautions 

 they may not only be kept alive, but they may be induced to develop 

 and to multiply. 



Simple preservation is possible in the case of Babesia and of 

 Trypanosomes, if the blood which contains them is prevented from 

 clotting by defibrination or by the addition of soda citrate. Laveran 

 and Mesnil recommend a solution of 5 grains of sodium chloride, and 

 5 grains of sodium citrate, in 1 litre distilled water, mixed in equal 

 quantities with the blood. The duration of life varies with the species ; 

 it is longest in the case of the Trypanosomes parasitic in cold-blooded 

 animals (fish) and in rats ; it is appreciably shorter in Trypanosomes 

 pathogenic to mammals. It depends, morever, upon temperature, 

 and, in the case of the Trypanosomes, unlike the intestinal Infusoria, 

 it is prolonged by cooling. For instance, Trypanosoma lewisi will live 

 in summer for four days only at room temperature, while it may be 

 kept for two months at a temperature of 5 to 7 C. Similarly, Babesia 

 bigemina and B. bovis will retain their vitality for two months, and 

 B. canis for twenty-five to thirty-nine days, if kept in a refrigerator. 

 But in all these instances, the organism is subject to certain changes 

 which lead eventually to decomposition. One of the most remarkable 

 of these changes is seen in B. canis when examined in blood taken, 

 under chloroform and shortly before death, from a strongly infected 

 dog. The blood should be thinned with about an equal part of normal 

 saline and kept at 27 C. or at room temperature. After about 

 eighteen hours, the sediment will be found to contain parasites 

 which, by the projection of raylike processes, have assumed a star- 

 like appearance. They give the impression of being quite rigid, but 

 prolonged observation in drop cultures will reveal slow changes of 

 form. The meaning of this starlike appearance is not known, the 



