HYPERSUSCEPTIBILITY AND IMMUNITY PRODUCED BY BACTERIAL 
PROTEIDS. 
Experimental studies with the bacterial proteids are of the greatest 
I importance on account of the practical uses to which results along this 
j line may lead. Our conviction that the phenomenon of hypersuscepti- 
i bility which we have been studying in the guinea pig has a deep sig- 
! nificance in general pathology, especially in the problem of immunity, 
j induced us to undertake an extensive series of experiments with pro- 
I teid extracts obtained from bacterial cell masses. Some of this work 
j is sufficiently advanced for us to record our results in part. 
I H^-persusceptibility may easily be induced in guinea pigs with pro- 
I teid extracts obtained from the bacterial cell. The first injection of 
1 most of the extracts used by us seems comparatively harmless to the 
j animal. A second injection of the same extract shows, however, that 
i profound physiological changes have taken place. A definite period 
i must elapse between the first and the second injection. The symptoms 
j presented by the guinea pigs as a result of the second injection 
I resemble those caused by horse serum. 
I The phenomenon induced by a second injection is followed (in cer- 
I tain cases) by an immunity to the corresponding infection. 
I These results strengthen our belief that the phenomenon of hyper- 
{ susceptibilit}^ has a practical significance in the prevention and cure 
I of certain infectious processes. It gives a possible explanation to the 
period of incubation of some of the communicable diseases. Is it a 
coincidence that the period of incubation of a number of infectious 
diseases is about ten to fourteen days, which corresponds significantly 
with the time required to sensitize animals with a strange proteid? 
In certain infectious diseases with short periods of incubation, such 
as pneumonia, the crisis which commonh^ appears about the tenth day 
I ^ may find a someAvhat similar explanation. It is evident that disease 
J processes produced hy soluble toxines, such as diphtheria and tetanus, 
do not belong to the category now under consideration. 
EXTRACT OF COLON BACILLUS. 
The extract from the colon bacillus in the following experiments 
was obtained as follows: 
A 2-day-old culture of £. coil communis in Dunham’s solution was 
used to heavily inoculate the surface of 81 large agar plates. These 
(31) 
