186 THE ACTION OF THE LIVING CELL 



of no avail; hence the conclusion was drawn that the 

 breeding stock through generations of domestication 

 had become unusually susceptible to the action of cy- 

 tost liberated during pregnancy. In order to test this 

 concept, it was decided to attempt immunization of 

 the guinea pigs to cytost. 



To this end, a cytost solution was prepared by ex- 

 tracting autolyzed guinea pig muscle with ten times 

 its weight of water, and after removal of the insoluble 

 material by centrifugation, the extract was passed 

 through a Berkefeld filter in order to insure sterility. 

 This preparation was then used directly for the im- 

 munization experiments reported below. 



In the first experiment twenty old females of the 

 same age and weight were taken from the breeding 

 stock which had been doing poorly. Breeding was 

 started on December 2, 1923. The animals were 

 divided into two groups of ten each. Beginning Feb- 

 ruary 4, 1924, each of the members of one group re- 

 ceived a series of seven subcutaneous injections of the 

 cytost extract, spaced one week apart, while the mem- 

 bers of the other group were held as controls. The 

 amount of the cytost extract used for each injection 

 was two or three minims. In this experiment it was 

 desired to ascertain the effect of the injections on the 

 mothers at the time of parturition and shortly there- 

 after. All the animals in both groups gave birth to 

 young atvarious times between February 3 and March 

 10. By the end of April all the members of the in- 

 jected series were still alive, whereas four of the mem- 

 bers of the controlled group had died on the follow- 

 ing dates: April 4, 12, 14, and 18. Subsequently all 



