HJEMOLYSINS AND ALLIED BODIES 439 



other hand, it was noted that the alexin of any animal's serum 

 could complete the reaction. If in the above experiment, for 

 example, some rabbit's serum had been added to the inactivated 

 serum instead of guinea-pig's serum, haemolysis would have fol- 

 lowed ; and if the rabbit's erythrocytes had not been thoroughly 

 washed free of adherent serum (containing alexin), the mere 

 addition of inactivated serum would have laked them. 



To these observations of Bordet on erythrocytes, might be 

 added, for the sake of interest, parallel ones by Pfeiffer, Metchnikoff, 

 and Bordet on the behaviour of cholera vibrios in the tissue 

 fluids. Under normal conditions these bacteria very quickly kill 

 a guinea-pig. It was found, nevertheless, that a normal guinea- 

 pig's serum can destroy a very small amount of cholera vibrios. 

 This, the serum does in virtue of an alexin which it contains. 

 The most important discovery from our point of view, however, is 

 that a sensitising substance could be developed in the serum and 

 the bactericidal power of the latter thereby greatly raised, so that 

 the cholera vibrios soon become immobile, and die when mixed 

 with it. If repeated sub-lethal doses of cholera culture were in- 

 jected in gradually increasing amount into the peritoneal cavity of 

 a guinea-pig, the serum of such an immunised animal became able 

 to destroy quantities of cholera vibrios which would otherwise have 

 killed many guinea-pigs; and, even if the immune serum were 

 injected into a normal guinea-pig, could endow the latter also with 

 resisting powers towards cholera infection. If the serum were 

 warmed, or left standing in the air for some time, it became 

 inactivated, and could be reactivated by the addition of normal 

 serum, or by placing it in contact with the peritoneum ; that is, 

 by adding an alexin to it. The cholera vibrios, in this process, 

 behave like erythrocytes. This important discovery in immunity 

 is given here to exemplify how close is the relationship between 

 haemolysis and bacteriolysis, and to show how important it is for 

 the bacteriologist to become acquainted with the former process, 

 which can be studied with ease in the test-tube, in order that he 

 may be able to infer the laws which govern the more practical, 

 but much more obscure process of bacteriolysis. 



Before proceeding further, it may be advantageous to 

 summarise briefly what we have already learned. The facts so 

 far, then, are as follows. The organism is normally endowed with 

 a certain amount of destructive power towards all cells foreign to 



