538 Chapter XVI 



intermediary substance (E. and M.), has the property of attaching or 

 fixing itself to the red blood corpuscles. 



The works on haemolysis, carried out during the last three years 

 by Ehrlich and Morgenroth on the one hand, and by Bordet on the 

 other, have allowed us to extend our study of the mechanism of the 

 action of the two substances on micro-organisms and on animal cells. 

 Ehrlich has extended his ingenious theory of antitoxins to the bacterio- 

 lytic substances, which he regards as side-chains detached from the 

 cells and capable of absorbing the toxins. In a series of remarkable 

 investigations, most of them carried out in collaboration with Morgen- 

 roth, Ehrlich has developed his theory which attempts to offer an 

 account of the essential mechanism which presides over the destruction 

 of micro-organisms and over the neutralisation of their poisons. This 

 theory is at present in full swing of development. Some of his points 

 contradict several of the conclusions in Bordet's works. Whilst the 

 latter maintains that the sensibilising substance becomes fixed as 

 [562] a mordant, Ehrlich regards it as entering into chemical combination 

 with the molecular group of the micro-organisms and of the animal 

 cells. According to Bordet, the alexin of the same species of 

 animal is always the same substance. Ehrlich energetically main- 

 tains the plurality of the alexins, to which he gives the name of 

 complements. 



This controversy has caused a most interesting exchange of views 

 and has led to experiments which are remarkably ingenious ; but it 

 must be admitted that as yet all the points in dispute are not 

 definitely settled. It is evident that we have here a new line of 

 research which promises most fruitful results for science. 



We have described in various chapters of this work the funda- 

 mental elements of Ehrlich's theory. Many think that this theory is, 

 in principle, antagonistic to the theory of phagocytosis, but we have 

 already observed that this view cannot be accepted. It is true that 

 Ehrlich maintains that the bacteriolytic and cytotoxic ferments 

 which we have called cytases (alexins or complements) circulate in 

 a state of solution in the blood plasma, whilst, according to the 

 theory of phagocytosis, they are found under normal conditions 

 inside phagocytes. But this view has nothing to do with the basis 

 of the theory of receptors, or of Ehrlich's side-chain theory, according 

 to which the antitoxin and certain other antibodies (intermediary 

 substance) are regarded as products detached from cells having an 

 affinity for the toxins and the microbial products. 



