causing Disease in Man in Nyasaland. 



125 



This curve was taken from a rat which was inoculated directly from the 

 naturally infected Dog 2033, and had therefore passed through no series of 

 rats. Yet the curve is the same as that shown in Chart 4 after two years' 

 passage through rats. 



It might be argued that this is really an infection with the larger of the 

 two hypothetical species, the one having a maximum of 28 microns. It is 

 to be regretted that this strain has died out, so that no further experimenta- 

 tion with it is possible. It would have been interesting to pass it through 

 other animals, in order to learn if any reversion to the short and stumpy 

 form would take place. But if it is not possible to do this with Strain II, 

 it is with Strain I, which was seen to change from a dimorphic type to a 

 practically mouomorphic type after two years' passage through rats. When 

 this almost monomorphic rat strain, as shown in Chart 4, is inoculated into 

 a dog, a reversion to the original dimorphic type is brought about, as will be 

 .seen from the following chart : — 



L 2 



