172 A MANUAL OF BACTERIOLOGY 



presence of two substances in the serum, one thermostable 

 and having the properties of an antigen (see p. 150), which 

 he terms " sensibilisogen/' and which on injection produces 

 its anti-body, " sensibilisin." The other substance is 

 thermolabile, and is termed " anti-sensibilisin," and 

 combines with sensibilisin whenever it meets with the 

 latter. Sensibilisin is particularly fixed by the cells of the 

 nervous system, and, according to Besredka, it is the 

 violent reaction between anti-sensibilisin and sensibilisin 

 in the nerve tissues which causes the serious disturbance 

 characteristic of anaphylaxis. When, therefore, a small 

 dose of serum (po,,-.-, 1 ,, c.c.) is administered, the sensibili- 

 sogen slowly forms sensibilisin. If a second dose of serum 

 is given twelve days or more after the first injection, the 

 anti-sensibilisin in it combines with the sensibilisin formed 

 by the first injection, and disturbance results. 



The reason why ana3sthetisation with ether when the 

 second injection is given prevents the symptoms of ana- 

 phylaxis developing is that the anaesthetic renders the 

 nerve cells insensitive to the reaction between the 

 sensibilisin and antisensibilisin. 



According to Richet, a " toxigen " is formed in the blood 

 or cells at the end of the incubation period and persists 

 for a long period. A toxic apotoxin or precipitin is formed 

 as a result of the interaction of toxigen with antigen, the 

 toxicity of which is further increased by combination with 

 the alexin of the blood. 



Bordet suggests that the union of anti-body and antigen 

 creates a complex which by adsorption monopolises certain 

 principles in the blood plasma which then becomes toxic. 

 Thus Wassermann and Reysser found that if guinea-pig 

 serum and kaolin, *an inert powder, be mixed and then 

 centrifuged, the intravenous injection of the fluid is 

 followed by symptoms closely resembling those of anaphy- 

 laxis. A weak agar jelly (0-05 per cent.) acts similarly. 



