PATHOLOGIC CHANGES 



557 



gut of mosquitoes, could not as easily obtain trypanosomes in pure 

 cultures as when cultivating them directly from the blood in which 

 they are generally the only live microorganisms. They devised the 

 following method, which gave satisfactory results: By means of a 

 glass spatula, made by drawing out the end of a glass rod, a little of 

 the mixed culture of flagellates and bacteria derived from the gut is 

 spread in a series of streaks over six Petri dishes. Ordinary agar 

 may be used in the first three dishes, since the desired dilution is not 

 attained until the last three. The Petri dishesjused must be so 

 constructed that they can be sealed tightly with a wide rubber band. 

 The sealed dishes are set aside at room temperature for ten to twelve 

 days. The last two plates frequently contain isolated colonies of 

 flagellates, which can be transplanted in the usual way to the blood 

 agar test-tubes. The flagellates occurring in mosquitoes under ordi- 

 nary circumstances are, however, not true trypanosoma but the 

 nearly related genera of crithidia and herpetomonas. 



FIG. 190 



Trypanosoma Lewisii, non-pathogenic rat 

 trypanosome. X 1000. (Author's prepara- 

 tion.) 



Trypanosoma Evansii, the cause of surra. 

 X 1000. (Author's preparation.) 



Pathologic Changes. It is very probable that pathogenic trypano- 

 somes cause disease by produing or setting free in the blood plasma 

 certain toxins, but practically nothing is known about the latter, 

 and they have not, like certain bacterial toxins and endotoxins, 

 been isolated. The most characteristic pathologic changes of try- 

 panosomiasis are generally a progressive anemia, with disturbances 

 of circulation, congestion, infiltration, and edema, and periodical 

 elevation of temperature, combined, in the later stages, with pareses 

 and paraplegias. The animals finally suffer from rapidly progressing 

 emaciation, which terminates fatally. Apart from the anemic changes 

 of the blood and the bone marrow, and from the presence of the 

 trypanosomes in the blood and other body juices, there are no morbid 



