IMMUNITY 9 



produce antitoxins in the sera of immunised animals. 

 The substances they call forth in the process are 

 directed against the invading organisms themselves, 

 in that they possess the power of destroying or of 

 causing the dissolution of the specific germs used in 

 their production. The therapeutic use of such anti- 

 bacterial sera has been disappointing, and their pro- 

 phylatic and curative action has been almost invariably 

 ineffectual, except when the sera could be brought 

 into direct contact' with the germs, as in epidemic 

 meningitis, when injected directly into the spinal canal. 

 It should also be effective in enzootic spinal paralysis 

 of equines, when used in like manner ; but, so far as I 

 know, an antiserum against this latter disease has not 

 been prepared. 



Antibodies and the Substances g'iving' Rise to 

 them. — In the foregoing section we have seen that 

 the process of active immunisation so changes the 

 animal body that it becomes highly resistant 

 against an infection to which it had formerly, in 

 many instances, been highly susceptible. This fact 

 started investigations to ascertain what part of the 

 animal body was responsible for these changes, the 

 result being that it was definitely proved that 

 the blood and blood serum were chiefly responsible. 

 During active immunisation the chemical com- 

 position of the blood serum is very little altered. 

 The first actual light was thrown upon the phenomena 

 of immunity by the investigations of Nuttall, Buchner, 

 and others, who not only demonstrated the power of 



