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50 THE BACTERIAL LEUCOLYSINS 



The leucolysins are substances which are formed by bacteria, 

 and which have the power of killing and dissolving, or partially 

 dissolving, the leucocytes of susceptible animals. Owing to the 

 comparative difficulty of obtaining emulsions of living leucocytes, 

 they have not been submitted to the same thorough examination 

 as have been the bacterial haemolysins ; but the important rela- 

 tions between the leucocytes and immunity lead us to believe that 

 they are of very considerable pathological interest. The first 

 to be described was that formed by the Streptococcus pyogenes, the 

 action of which on the living leucocytes was shown by an ingenious 

 experiment to occur in vitro, and to be neutralized by means of 

 antileucolysin, this being one of the earliest proofs that toxin and 

 antitoxin form a chemical combination, and that the preventive 

 and curative effects of the latter are not due to some profound 

 influence on the tissues of the living body, by which they are 

 rendered immune before the toxin can attack them. The method, 

 invented by Neisser and Wechsberg, is based on the fact that 

 living leucocytes have the power of deoxidizing and bleaching a 

 solution of methylene blue. When a solution of the products of 

 growth of streptococci is added to an emulsion of living leuco- 

 cytes, together with a little of the dye, and a layer of liquid 

 paraffin added to prevent the further access of air and subsequent 

 oxidation of the methylene blue, the colour no longer disappears, 

 showing that the leucocytes have been killed. If, however, a 

 suitable amount of antileucolysin (obtained by injecting the 

 filtered products of the streptococci into an animal) be added to 

 the mixture the colour disappears, showing that the leucocytes 

 have been protected from the action of the leucolysin, which has 

 now been neutralized by the serum. 



The action of the leucolysins can also be studied microscopi- 

 cally in vitro, when the cells are seen to become more transparent, 

 and their nuclei to become more indistinct, and ultimately to 

 disappear. The dissolving leucocytes look very much like those 

 found in pus. 



Leucolysins are formed by the Streptococcus pyogenes, the staphy- 

 lococcus, and B. pyocyaneus, and probably by other organisms. 



The bacterial hsemolysins are an interesting group of substances 

 which are closely allied to the exotoxins in their reactions, but 

 are little toxic, if at all. The most toxic appears to be that of 

 Streptococcus pyogenes, to which some observers, though not all, 

 attribute feeble poisonous powers when injected into animals. 



