228 BACTERIOLYSINS 



organism with which the animal has been immunized. The serum of animals 

 immunized with the typhoid bacillus for instance is bactericidal only for the 

 typhoid bacillus and is totally devoid of action on the cholera vibrio, and, 

 vice versa, an anticholera serum is not bactericidal for the typhoid bacillus. 



The bactericidal action of immunized serums is rapid and at its maximum 

 at 37 C., feeble at the ordinary temperature of the laboratory and altogether 

 paralyzed at C. 



The analysis of the phenomena of bacteriolysis may now be pushed a step 

 further and an attempt made to investigate the mechanism by which bacterio- 

 lysis occurs. 



Mechanism of bacteriolysis. 



Suppose the serum of a guinea-pig immunized with the cholera vibrio be 

 heated to 55 C. and then mixed with a culture of the vibrio. Bacteriolysis 

 no longer takes place, though the agglutinating properties of the serum 

 remain unaffected (Bordet). 



The heated serum, however, has not altogether lost its bactericidal pro- 

 perties; for, if to the mixture of vibrios and heated serum a small quantity 

 of serum from a normal animal be added, bacteriolysis occurs at once the 

 heated serum is re-activated. 



It may therefore be concluded that the serum of the immunized animal 

 contains two substances : 



(i) One of which is not destroyed by being heated at 55 C. or, in other words 

 is thermostable at 55 C. and which is only present in the serum of immunized 

 animals. 



(ii) The other of which is destroyed by heating to 55 C. or, in other words, 

 is thermolabile at 55 C. and which is present also in the serum of normal 

 animals. 



These two substances when present together cause bacteriolysis but either 

 the one or the other acting alone has no action on the vibrio. Let us con- 

 sider now the part which each of these substances plays. 



A. Immune body (Sensibilisatrice). The thermostable substance is, as has 

 been said, present only in the serum of immunized animals and is a product 

 of immunization [hence the term immune body generally used in England]. 

 And, further, it is specific and acts only on the organism which was used for 

 immunization. 



Experiment. Treat an emulsion of cholera vibrios with anticholera serum heated 

 to 55 C. and then add a little normal rabbit serum. The vibrios will be bac- 

 teriolyzed. 



Repeat the experiment using instead of cholera vibrios, typhoid bacilli. Treat 

 the typhoid bacilli with heated (55 C.) anticholera serum and then add the normal 

 rabbit serum. No bacteriolysis takes place. 



The immune body in contact with its corresponding micro-organism is 

 fixed by the organism in the same way that a mordant acts on a fabric. 



Experiment. Leave a mixture of cholera vibrios and heated anticholera serum 

 for half an hour at 37 C. Centrifuge to separate the vibrios, wash the latter with 

 normal saline solution and then add a little fresh normal rabbit serum to the vibrios. 

 Bacteriolysis takes place. 



This experiment justifies the view held by Bordet that the immune body 

 sensitizes the organisms to the action of the thermolabile substance present 

 in normal serum just as a mordant sensitizes a fabric to the action of a dye. 

 Hence the use in France of the word Sensibilisatrice to denote the immune 

 body. The immune body is only destroyed by heating it at 65-70 C. 



Sensitized micro-organisms, that is to say, organisms which have been 



