ANTIBODIES 



375 



when injected into the blood causes the appearance in the 

 blood of a substance known as a precipitin, which precipi- 

 tates that protein. This reaction is highly specific. When 

 the serum of an animal of species A is injected into an animal 

 of species B, the latter develops a precipitin for the serum 

 of species A only. Upon this fact is based an important 

 medico-legal test for human blood. There are also agglu- 

 tinins which cause a clumping together of bacteria. Further, 

 when foreign cells are introduced there are developed anti- 



T0XOPHOR.E GROUP 



HrtPTOPHORJi GROUP 



RECEPTOR. 



PRDTOFL/iSMlC 

 MOLECULE . 



^^ 



Fig. 72. 



bodies — cytolysins — which destroy those cells. The most 

 important of these are the hsemolysins which are produced 

 on the injection of foreign red blood corpuscles. The 

 mechanism in this case is rather comphcated. Let us take 

 a specific example. 



The red blood corpuscles of the rabbit added to the normal 

 serum of the goat are hsemolysed, but if the serum has 

 been previously heated to 60° ha3molysis does not occur. 

 If, however, the red blood corpuscles of the rabbit be added 

 to the heated serum of the goat together with normal 

 (unheated) rabbit's serum, haemolysis results. Ehrhch be- 

 lieves, therefore, that there are two substances responsible, 



