THE RAT TRYPANOSOME 



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been able to sub-cultivate the organisms for 22 generations ; the cultures are 

 pathogenic and contain living, motile Trypanosomes. In old cultures rosette 

 forms appear ; these become more and more numerous and the culture dies 

 after about 15-20 days in the warm incubator, but at a much later period if 

 kept at the temperature of the laboratory. 



FIG. 390. Multiplication forms of Trypanosoma lewisi. (After Laveran and Mesnil.) 1, adult 

 trypanosome ; 2, a trypanosome about to divide ; 3, rosette forms ; 4, young forms. 



The size of the Trypanosomes varies considerably in the same culture. Some may 

 be 50-60/z long while others do not exceed 1-2/x in length including the flagellum. 

 This fact explains why it has been found possible to infect rats with the filtrates 

 of cultures passed through a Berkefeld bougie. 



The shape also of the Trypanosomes is very varied, and pyriform, rounded, and 

 delicate fusiform parasites are seen. Numerous agglomerated masses occur in 

 which the flagella are always directed towards the centre. 



Agglomeration (Agglutination).- Laveran and Mesnil have shown that 

 Trypanosoma lewisi will live much longer in blood kept in the ice chest 

 (5-7 C.) than at the temperature of the 

 laboratory. In infected rat blood mixed 

 with an equal volume of saline solution 

 and defibrinated Trypanosomes will retain 

 their vitality for 30-50 days if kept in the 

 cold, whereas if kept at a temperature of 

 15-20 C. they will die in about 3 days. 



In blood kept in this way, Trypanosomes 

 at first preserve their normal appearance 

 and are very motile. But after about 3 

 days agglomeration commences : two Try- 

 panosomes unite by their aflagellar ex- 

 tremities, others join them and form a sort 

 of rosette, the flagellated ends of all remain- 

 ing free and motile ; the number of parasites 

 entering the agglomerated mass increases 

 daily. The blood is pathogenic so long as 

 it contains motile parasites. Agglomeration 

 occurs much more rapidly in hanging drops of the blood kept at laboratory 

 temperature : under these conditions agglomerated masses may be observed 

 after 24 hours. 



FIG. 391. Agglomeration of 

 Trypanosoma lewisi. 



