204 THE ACTION OF THE LIVING CELL 



autolyzed mouse tissue with forty times its weight of 

 water proved the most serviceable. Mice were able 

 to withstand a series of several injections of 0.25 cc. of 

 such an extract without any apparent harm. 



A series of mice were immunized by means of six in- 

 jections of 0.25 cc. of such a cytost preparation, spaced 

 10 days apart. The second series received eight injec- 

 tions of 0.06 cc. of the cytost preparations, spaced one 

 week apart. These two groups of mice, together with 

 untreated controls, were kept in spacious cages under 

 identical conditions, and allowed to breed. The effi- 

 cacy of the immunizing treatment was judged by the 

 mortality rate of the offspring of the three groups. 

 During the period of observation, which extended 

 over several months, 30% of the young born of non- 

 immunized mothers died; whereas in the two im- 

 munized groups the mortality rate of the young was 

 5% and respectively. 



The lower mortality rate found in the cytost- 

 injected animals indicates that the immunization pro- 

 cedure adopted was actually effective. As it had been 

 observed that during the winter months many mice 

 died of pneumonia when their cages were placed on 

 the floor of the breeding room so as to be exposed to 

 draughts of cold air, cages containing immunized and 

 non-immunized mice were kept on the floor through- 

 out the winter and spring. Under these conditions 

 many of the non-immunized animals died, although 

 all the immunized lived through this period. This 

 difference was especially noticeable in the case of the 

 newly born, for the mortality of the offspring of the 

 non-immunized mothers amounted to 50%. 



On comparing the young born of the two groups 



