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.”’ 
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 
