ON THE MODE OF ACTION OF PREVENTIVE SERA. 91 



of the experiments which we have mentioned and added others, 

 and as we shall see presently he has drawn certain conclusions as 

 to the mechanism of passive immunity which are in part similar 

 to our own. This confirmation is gratifying, but we shall not con- 

 sider further such experiments and conclusions as have already 

 been mentioned. We shall consider more particularly the new 

 facts and interpretations which he has offered. First of all Gruber 

 finds that B. coli and B. typhosus react under similar conditions in 

 the same way as do the vibrios, that is to say, they lose their motility 

 and become clumped. 



Gruber thinks that a swelling and viscosity of bacteria will 

 explain their clumping by preventive sera. He thinks, moreover, 

 that this viscosity actually produces the collection and adhesion 

 of separated organisms into clumps. On this account Gruber calls 

 those substances that produce clumping "agglutinins." However 

 fitting this term may be, we must consider first whether the swell- 

 ing and viscosity of bacteria can explain a collection and clumping 

 of disseminated micro-organisms. It is quite conceivable that vis- 

 cosity may prevent the separation of bacteria already clumped, 

 but it is not quite so clear how this change can bring them together, 

 particularly when we are dealing with non-motile organisms. 

 Tetanus bacilli and streptococci are clumped by sera; and motile 

 organisms (such as the cholera vibrio) are clumped, even when they 

 have been killed with chloroform and so lost their motility. 



When cholera vibrios are mixed with heated cholera serum 

 clumping occurs, but no granular transformation is to be noted. 

 The clumping, however, occurs very well, even when serum that has 

 been kept for some time is used ; clumping, moreover, occurs very 

 rapidly, whereas the metamorphosis takes some time. Vibrios that 

 have been rapidly brought together into definite masses when colored 

 by the usual stains show no distinct alterations.* 



It is evident then that the viscosity of clumped bacteria cannot 

 be directly demonstrated and consequently must be regarded as 

 purely hypothetical. This idea of a surface modification of bacteria 

 which Gruber regards as certain becomes less admissible when we 



* When about to send these pages to the press we found that Pfeiffer has noted 

 that same fact in the last number of the Deutsche medicinische Wochenschrift, 

 April 9, 1896. 



