NATURAL RESISTANCE 177 



did not differ very greatly, it seems likely that the 

 tolerance to cytost exhibited by both groups of kit- 

 tens is directly traceable to the fact that their mothers 

 had been actively immunized. The length of life of 

 the kittens born of immunized mothers is summarized 

 below. (Turck, 1923.) 



The fact that all the kittens in these two groups 

 lived for a comparatively long period under condi- 

 tions known to be rapidly fatal to kittens implies that 

 the resistance of these animals was greater than is 

 usually the case with young kittens, and from the very 

 nature of the experiment can only be attributed to the 

 fact that the mothers had been actively immunized to 

 cytost. This fact suggests that the immunized mothers 

 were able to transmit their acquired immunity to their 

 offspring. This perhaps is simply another way of 

 stating the well-known fact that vigorous healthy ani- 

 mals usually give birth to young which as a rule have 

 a greater natural resistance than do the offspring of 

 normally inactive animals. 



Although the latter statement by itself conveys noth- 

 ing new, it is of singular interest that immunization 

 of the mothers to cytost enables us to insure the pro- 



