ON THE NATURE OF TOXINS 53 



perhaps this is the reason why slight staphylococcic infections in 

 man are not associated with marked haemolysis. 



Streptocolysin is formed in forty -eight hours when a virulent 

 streptococcus is incubated in broth containing blood-serum or 

 ascitic fluid, and it is a remarkable fact that the nature of the 

 serum used modifies the lysin produced. Thus if ox serum be 

 employed the lysin will act on the corpuscles of the guinea-pig, 

 rabbit, and man, but not those of the ox or sheep ; whilst all 

 these will be dissolved by that grown in broth to which human 

 serum has been added. 



Streptocolysin is less thermolabile than tetanolysin and staphy- 

 lolysin, requiring an exposure of ten hours to 55 C. or of two 

 hours to 70 C. for complete destruction. 



The other bacterial haemolysins i.e., those produced by the 

 B. pyocyanens, B. typhosus, and B. coli are quite different from 

 the foregoing in being thermostable. Thus pyocyanolysin re- 

 sists a temperature of 120 C. for thirty minutes. Typholysin 

 appears to be less resistant, but is definitely thermostable. 

 Colilysin is as stable as pyocyanolysin ; it is not destroyed by 

 a temperature of 120 C. for half an hour, and does not undergo 

 spontaneous weakening for months. It is obvious that these 

 substances are different in character from the other haemolysins 

 and exotoxins, and the fact that (in the case of pyocyanolysin and 

 colilysin, the most heat-resistant of the group) the haemolytic 

 property of the culture only appears when it becomes strongly 

 alkaline and is roughly parallel in degree to the amount of alka- 

 linity, has led some to think that the substances are not the true 

 haemolysins at all, but merely simple alkaline chemical products 

 of growth ; and this is corroborated by the fact that much of the 

 haemolytic power is taken away on neutralization with a weak 

 acid. It appears that this is not the case, since in a culture of 

 B. coli at a temperature of 23 C., the alkalinity reaches its maxi- 

 mum on the fifth day, whilst the haemolytic property does not 

 appear until later. The subject requires further investigation, and 

 at present it is advisable to disregard these substances which differ 

 so much from their allies. 



The chemical nature of the exotoxins has been the subject of 

 much controversy, and is still very imperfectly understood. It 

 will not be discussed at great length, since from the point of 

 view of immunity it is not of very great importance. 



The close analogy between the bacterial exotoxins and certain 



