288 IMMUNO-CATALYSIS 



the blood with the products of injured tissue. They found that this 

 plasma rich in fibrinogen constituted an excellent substrate for 

 "ferment-fibrin" or thrombin as we know it now. It clots rapidly when 

 treated with a trace of fresh serum of different species of animals, 

 guinea pig, rabbit, sheep, dog, etc. The serum of birds clotted this 

 plasma very slowly because of the low clotting enzyme (thrombin) 

 content of bird's blood. 



The thrombin activity of sera is destroyed when heated at 58.5°C. 

 for 45 minutes. When a mixture of fresh rabbit serum and normal 

 guinea pig serum (inactivated at 58.5°C.) was added to avian plasma 

 the latter clotted because of the presence of enzyme in the fresh rabbit 

 serum. In contrast, a mixture of fresh rabbit serum with inactivated 

 anti-rabbit immune guinea pig serum was incapable of clotting the same 

 avian plasma. This showed that anti-rabbit immune guinea pig serum 

 neutralized the enzyme in the fresh rabbit serum. The presence of 

 an anti-enzyme antibody in immune guinea pig serum resistant to a 

 temperature of 58.5° C. was thus demonstrated in the above, as well as 

 in the following series of experiments. 



From Table XV it is to be seen that the enzyme present in fresh 

 rabbit serum and responsible for the clotting of the avian plasma was 

 specifically inhibited by homologous immune guinea pig serum. The 

 complete inhibition of the enzyme present in one volume of fresh 

 rabbit serum required six volumes of immune guinea pig serum. If 

 instead, three volumes of immune serum were used the inhibition of 

 the enzyme was marked but not complete. 



The immune guinea pig serum had no inhibitory effect on the en- 

 zyme of fresh normal serum of dog or sheep, showing a high degree of 

 specificity. 



Immunization of the rabbit with guinea pig serum produced in the 

 rabbit antibodies which likewise neutralized the plasma clotting 

 enzyme of the guinea pig serum. It had no inhibitory effect on the 

 enzyme of normal rabbit serum in the same way that anti-rabbit im- 

 mune guinea pig serum was ineffective against the enzyme of normal 

 guinea pig serum. 



