67 
resistance to a certain class of diseases. W e can not escape the con- 
viction that further studies upon the phenomenon of hypersuscepti- 
bilit}" will have an important bearing upon the prevention and cure of 
certain infectious processes. The hj-persusceptibility obtained by 
bacterial proteids and the subsequent immunity furnishes data for this 
belief. 
From our work upon the proteid substances of animal and vegeta- 
ble origin, it was but a step to the albuminous content of the bacte- 
rial cell. Experimental studies upon the bacterial proteids are of the 
greatest importance on account of the practical uses to which results 
along this line may lead. 
i Hypersusceptibilit}' may easily be induced in guinea pigs with pro- 
teid extracts obtained from the bacterial cell. The first injection of 
the extracts used by us seems comparative! v harmless to the animal. A 
second injection of the same extract shows, however, that profound 
! physiological changes have taken place. A definite period must elapse 
between the first and the second injection. The s 3 "mptoms presented 
I by the guinea pig as a result of the second injection resemble those 
caused b}- horse serum. 
I The phenomenon induced by a second injection is followed, in cer- 
tain cases, by an immunity to the corresponding infection. 
, These results give a possible explanation of the period of incu- 
bation in some of the communicable diseases. Is it a coincidence 
! that the period of incubation in a number of infectious diseases is 
about ten to fourteen days, which corresponds significant!}" with the 
time required to sensitize animals with a strange proteid ? In certain 
infectious diseases with a short period of incubation, such as pneu- 
j monia, the crisis, which commonly appears in about ten days, may find 
", a somewhat similar explanation. It is evident that diseased processes 
I r ; produced by soluble toxines, such as diphtheria and tetanus, do not 
!. belong to the category now under consideration. 
1 The phenomenon of hypersusceptibility has been produced in the 
guinea pig by extracts obtained from the colon bacillus, yeast, hay 
bacillus, anthrax, tubercle bacillus, and the typhoid bacillus. The 
hypersusceptibility produced by the colon and typhoid I)acillus was 
, followed by a definite immunity to the corresponding infections. In 
■ the case of anthrax, howeA^er, immunity does not follow hypersus- 
! ceptibility to the anthrax proteid. We are, therefore, not dealing 
with a general laAA" applicable to all infections, but with certain limi- 
^ ‘ tations as in the case of antitoxic immuniW. 
^ ‘ 
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