202 OMENTAL PLAGUE chap. 



the result of which is the development in them of various 

 new substances. Amongst these, two at any rate have 

 been studied carefully : (a) agglutinins ; and (b) lysins, or 

 germicidal or immunising substances. I do not discuss 

 here — the matter being outside this treatise — the different 

 theories that have been put forward as to the probable 

 nature of these substances, viz. whether they are ferments 

 (Roux, Emmerich) or are some highly and complexly 

 constituted organic bodies other than ferments (R. Pfeiffer, 

 Ehrlich, and others). I am content to give consideration 

 to their mode of action as observed in actual experiment. 



The Agglutinins. — Bordet and Gruber were the first to 

 show that the blood serum of an animal subjected to repeated 

 injections with the typhoid or cholera microbe sooner or 

 later (usually in about a fortnight) acquires a new property : 

 that when a small quantity of the serum is added to an 

 emulsion of the typhoid or the cholera microbe respectively 

 the microbes soon lose their motility, are i attracted 

 together, and become at the same time " agglutinated " 

 or " clumped/' so as to form smaller or larger masses. 

 These, on account of their weight, gradually sink to the 

 bottom of the tube in which the emulsion is contained, 

 and the previously turbid fluid thus becomes clear. This 

 process of "clumping" or "agglutinating" has been 

 also studied in other cases besides those of the typhoid 

 bacillus or the cholera vibrio, and it has been shown 

 that the phenomenon is of a fairly general nature ; that 

 the blood of an animal which has been repeatedly injected 

 with a given microbe — pathogenic or non-pathogenic — 

 acquires the power to " agglutinate " an emulsion of the 

 particular microbe with which it has been, so to speak, 

 " prepared." It had been further shown that the degree 



