VACCINATING INJECTION 47 



diminution of toxicity with the minimum loss of 

 curative power, it is necessary not to exceed 59°- 

 60*^ C, a temperature at which antibodies generally 

 remain intact. 



The following is a short resume of experiments 

 made on the above lines. We chose a very toxic 

 serum in order to be able to follow the progressive 

 diminution of the toxicity, in proportion to the 

 duration of the heating. 



This unheated serum was of such virulence that 

 0-025 c.c. injected by the subdural route either killed 

 the guinea-pig in a few minutes, or set up very serious 

 anaphylactic symptoms, from which the guinea-pig 

 only recovered by degrees. 



After heating to 60° C. for an hour on three successive 

 days, the toxicity of the serum was as follows : 



0-25 c.c. Certain death. 



o-i c.c. Symptoms very serious, but not followed 

 by death. 



0-05 c.c. No symptoms. 



After heating to 60° for an hour on five successive 

 days : 



0-25 c.c. Certain death. 



0-125 c.c. Symptoms serious, but transitory. 



0-0625 c.c. Hardly any symptoms. 



After heating to 60° C. for an hour on seven succes- 

 sive days, the results were the same as above. 



It will be seen, therefore, that even moderate but 

 prolonged heating is capable of reducing the toxicity 

 of the serum to one fourth or fifth of its virulence. 



In the same way the toxicity undergoes an appre- 

 ciable modification with a temperature of 56" C. It 

 follows, indeed, from our experiments that serum 

 which has been heated on three successive days to 

 56° C. for an hour, and on the fourth day for two 

 hours, is three times less toxic than the same serum 

 when not heated. 



