842 PATHOGENIC MICROORGANISMS 



suspending them in salt solution, killing at 56 C. for one hour, 

 then adding one-half per cent carbolic acid. Other observers, like 

 Nicoll and Vincent 18 killed without heat, by the addition of carbolic 

 acid. Extracts of the cholera spirilla have also been used in various 

 ways. Strong 19 grows cholera organisms on agar, takes them up 

 in salt solution, kills at 60 and then allows the suspensions to stand 

 in the incubator for about five days, subsequently filtering through 

 a Berkefeld candle. This filtrate is used for -inoculation, after its 

 sterility has been determined by culture. Wassermann 20 has used 

 materials prepared by precipitation of cultures with alcohol. Cas- 

 tellani 21 during the last ten years has prepared what he calls a 

 T. A. B. C., or tetravaccine, which is made by mixing agar cultures 

 of typhoid, paratyphoid "A," paratyphoid "B," and cholera in 

 saline emulsion. The emulsion is killed with one-half per cent 

 carbolic acid, preserved for twenty-four hours in this form at room 

 temperature and then standardized by the usual counting chamber 

 method so that 1 c.c. should contain five hundred thousand typhoid, 

 250 thousand paratyphoid "A," 250 thousand paratyphoid "B," 

 and two thousand million cholera spirilla. 0.5 c.c. of this is injected, 

 three doses being given within two weeks. This is the vaccine which 

 we used on the Serbian Army during the war. 



The principle underlying all these procedures seems to us to 

 be the same, in that they consist of introducing, subcutaneously, 

 substances derived from the bodies of cholera spirilla. And since 

 the cholera organisms probably do not live very long after sub- 

 cutaneous introduction, it is not likely that it makes very much 

 difference whether attenuated living cultures, or dead cultures are 

 used. 



As far as the available statistics show at the present time, cholera 

 vaccination is of distinct value. This has been the judgment of 

 those who have scrutinized Haffkine's immunization experiments, 

 as well as those who have observed more recent army experiences. 

 The following table which we used in our Nelson article, again 

 taken from Violle, will give some idea of the comparisons made 



18 Nicoll and Vincent. Cited from Violle loc. cit. 



19 Strong. J. of Exp. Med., Vol. 8, p. 229, 1905. 



20 Wassermann. Festschr. E. Koch, Jena, 1903. 



21 Castellani and Chalmers, Manual of Tropical Medicine, W. Wood & Ho, 

 New York, 1919. 



