ESSAYS ON BACTEEIOLOGY. 85 



ing power in the animal. Finally, a condition is 

 reached in which the animal is able to resist enormous 

 quantities of the poison. The blood is now drawn, 

 allowed to clot, the serum removed, and, after filtra- 

 tion and the addition of a small per cent, of antiseptic, 

 is ready for use. This serum it is which seems to con- 

 tain the antitoxic agent, and wliose injection into a 

 susceptible animal confers upon that animal, for a 

 variable and limited time, the resisting power of the 

 animal from which it was taken. This serum it is, 

 also, which is injected into human beings exposed to 

 or already sick with diphtheria. 



I shall not now array the statistics which have been 

 presented for and against this new treatment, which 

 we owe chiefly to the labors of Behring and Kitasato 

 in Geirraany, and Roux in France. Perhaps the 

 most significant , and most influential are those 

 published by Yirchow, summarizing the experi- 

 ence in the Emperor and Empress Frederic Hos- 

 pital in Berlin. During a given period between five 

 and six hundred cases of proven diphtheria were in 

 the hospital. Of these over three hundred were 

 treated with the serum, with a mortality of about 13 

 per cent. Over two hundred, treated without the 

 serum, gave a mortality of about 4Y per cent. Equally 

 significant was the fact that when, at times, the serum 

 treatment was suspended the mortality at once rose, to 

 fall again promptly with the resumption of the anti- 

 toxin therapy. The known conservatism of Virchpw 



