INFECTION WITH ANIMAL PARASITE 53 



the number of the parasites, could hardly be accounted for in any 

 other way, while the mere destruction of the red cells itself could be 

 explained by the manifest proteolytic activity of the parasite and 

 consequent changes in the osmotic tension in the cell. In trypanoso- 

 miasis the late symptoms at least (sleeping sickness) would suggest 

 a toxic cause, and in relapsing fever the entire symptom complex 

 is toxic in character. As I have said, however, we have no definite 

 knowledge on the subject, which is, no doubt, owing to the fact that 

 until quite recently we were unable to cultivate the parasites in 

 question as we would bacteria, and could hence not study the 

 products of either their growth or disintegration. 



