THEORIES OF IMMUNITY. 



If this be heated to 55° C, for one-half hour, 

 the complement is destroyed, and the comple- 

 ment molecule (H+L+X) no longer exists. 

 The serum therefore is incapable of exercising 

 its bacteriolytic property. If now the fresh 

 serum of an ox, rabbit, or pig (containing of 

 course fresh complement (H+L+X)) be added, 

 the same constituents as at first would exist in 

 the anti-typhoid serum, and the bacteriolytic 

 power would be restored. 



The various facts brought forward show that 

 one of the difficulties that may arise in the treat- 

 ment of diseases of the second order (like ty- 

 phoid fever, cholera, and plague) is in the fact 

 that much more immune body may be formed 

 than there is complement to help make active, 

 and it is possible that this may be the explana- 

 tion of the poor results obtained with antitoxic 

 sera in the diseases just spoken of. Just how 

 this difficulty is to be met has not been shown, 

 but it is true that the apparently simple thing 

 to do, the addition of fresh sera (containing more 

 complement) does not fulfil the requirements, 

 at least so far as experiments have yet gone. 



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