BACTERIOLYSIS AND ALLIED PHENOMENA 179 



of two bodies, and therefore of the validity of Neisser and 

 Wechsberg's explanation, antibodies and other substances have 

 their action diminished or suspended when they are present in 

 excess ; thus with a great excess of agglutinin there may be no 

 agglutination. And Detre and Sellei have shown that phenomena 

 which are apparently somewhat similar occur in the haemolysis 

 induced by mercury perchloride. 



In view of the important role in immunity which must be 

 ascribed to alexin and, as we shall see, it acts not only as a 

 bacteriolytic agent, but also plays a part of great importance in 

 phagocytosis an inquiry into its source becomes of paramount 

 importance. The theory was put forward very early in the 

 history of the subject, before the mode of action of alexin and its 

 dependence on immune body were understood, that it was derived 

 from the leucocytes, either by a process of secretion or disintegra- 

 tion. This was first suggested by Hankin, who prepared a 

 substance having bacteriolytic powers from extracts of the 

 lymphatic glands and spleen ; this, however, was probably not a 

 true alexin. Experimental evidence of a more convincing kind 

 soon followed ; thus Denys, Van de Velde, and others, caused the 

 production of aseptic exudates rich in leucocytes by injecting 

 various irritants into the pleural cavity of animals, and found that 

 the more leucocytes present the greater the bactericidal action of 

 the fluid. Buchner performed similar experiments, using aleuron 

 emulsions to produce the exudate, and found that the richly 

 cellular material had a greater bactericidal effect than blood or 

 serum ; in his experiments he avoided the possibility of phago- 

 cytosis (which probably explained some of the results of other 

 investigators) by freezing the fluids before determining their 

 potency. A large number of other researches were made about 

 this time, and all pointed in the same direction, and in the early 

 nineties it was fairly generally held that the alexins were given off 

 in some way or another by the leucocytes. This view was strongly 

 held by Metchnikoff, whose microcytase must be regarded as 

 identical with the alexin or complement which acts on the 

 bacteria; and this microcytase he holds to be produced by the 

 polynuclear leucocytes under certain circumstances, which will be 

 discussed subsequently. 



With the discovery of the compound nature of the bactericidal 

 substances the question entered on a new phase, and new methods 

 of investigation were seen to be necessary. Since then very 



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