THE BACILLUS OF WHOOPING-COUGH. 479 



whooping-cough exudate which contains numerous organisms, in 

 the eye of the rabbit, only very slight growth occurs; the aqueous 

 humor remains limpid and white and intense weeping takes place, 

 together with an excessive conjunctival congestion. Injection 

 of a small amount of pure culture produces the same lesions, the 

 gravity of which is surprising in view of the fact that there is little 

 or no multiplication of organisms. If such a course goes on in the 

 bronchi, it is easy to understand the accesses and their persistence 

 even when the growth of the organism decreases. 



The authenticity of this bacillus as the causal agent in whooping- 

 cough rests in large part on the circumstances in which it is found, 

 namely, the excessive growth of the organism in pure culture during 

 the initial period of diseases in young children who have never 

 before been ill. The principal argument, however, in favor of 

 this organism appears to us to be furnished on studying the specific 

 properties of the serum. The serum of individuals that have never 

 had whooping-cough, or who have had it a long time before, does 

 not agglutinate the bacillus even in low dilution. The sera of 

 children that have recently recovered from the disease has a mod- 

 erate agglutinating property which is constant and evident. The 

 most remarkable fact, moreover, is the intensity of sensitizing 

 property in such sera. To demonstrate it we have used our accus- 

 tomed method of alexin fixation. 



The essentials of this method which we demonstrated in 1901 

 and employed to demonstrate the presence of sensitizers in many 

 immune sera, are well known.* It has since been employed by 

 numerous experimenters — Lesourd, Lambotte, Fassin, Cohen, and 

 more recently by Wassermann and Bruck.f One of us established 

 in 1900:|; that specific sensitizers which are active against bac- 

 teria or red blood cells endow the element which they attack with 

 the new property of absorbing alexin energetically. If a mixture 

 of alexin (fresh animal serum), of the substance under considera- 

 tion, and of a suitable sensitizer (that is, immune serum heated to 

 56 degrees), is prepared in suitable proportions it is found that after 

 a certain period the alexin has disappeared from the fluid. Con- 



* See p. 217. 



t The historical account of our method, by Wassermann and Bruck, of which 

 they have made considerable use, is remarkably brief. 

 % See p. 186. 



