DIPHTHERIA BACILLUS. 359 



how it is turned for the purpose of comparison with 

 previous results, the conclusion reached is always the 

 same namely, there has been an average reduction of 

 mortality from the use of antitoxin in the treatment of 

 diphtheria of not less than 50 per cent., and under the 

 most favorable conditions a reduction to one-quarter, 

 or even less, of the previous death-rate. This has 

 occurred not in one city at one particular time, but in 

 many cities, in different countries, at different seasons 

 of the year, and always in conjunction with the intro- 

 duction of antitoxin serum and proportionate to the 

 extent of its use. 7 ' 



The Production of Diphtheria Antitoxin for Therapeutic 

 Purposes. As a result of the work of years in the 

 laboratories of the Health Department of New York 

 City, the following may be laid down as a practical 

 method : 



The strongest diphtheria toxin possible should be 

 obtained by taking a very virulent culture and grow- 

 ing it under the conditions described on page 345. 

 The culture, after a week's growth, is removed, and 

 having been tested for purity by microscopical and 

 culture tests is rendered sterile by the addition of 10 

 per cent, of a 5 per cent, solution of carbolic acid. 

 On the following day the sterile culture is filtered 

 through ordinary sterile, filter-paper and stored in 

 full bottles in a cold place until needed. Its strength 

 is then tested by giving a series of guinea-pigs care- 

 fully measured amounts. Less than 0.01 c.c., when 

 injected hypodermatically, should kill a 250-gramme 

 guinea-pig. 



The horses used should be young, vigorous, of fair 

 size, and absolutely healthy. Vicious habits, such as 



