IMMUNITY" AND ADAPTATION. 145 



Some facts are known in regard to the place of origin of such 

 "antibodies" and in regard to the conditions which favor or 

 inhibit their appearance. From a certain point of view we may 

 at present perhaps distinguish three types of reactions. 



1. If at certain intervals a solution of abrin is dropped into the 

 conjunctival sac of an animal, substances are formed in the con- 

 junctiva to which the abrin was applied, which are able to neutral- 

 ize the injurious effect of abrin. In this case a local response of 

 the cells on which the substance acted, has taken place. 



2. If we inject substances, as cultures of the cholera vibrio 

 subcutaneously, intraperitoneally or intravenously, antibodies are 

 produced in organs far removed from the place of injection, as 

 for instance in the spleen and in the bone-marrow. The mere 

 injection of these substances is sufficient to produce this result. 



3. There exists a third type of reaction, which seems to be of 

 a more complicated character than the forementioned ones, and 

 which hitherto has been regarded as a totally different process, 

 but which seems to be essentially of a similar character. The 

 normal pancreas, which is the source of several hydrolytic fer- 

 ments usually does not produce lactase, a ferment capable of 

 splitting the disaccharid lactose. If, however, an animal receives 

 with its food a certain quantity of lactose, for instance in the form 

 of milk, lactase is secreted by the pancreas. The introduction of 

 a carbohydrate into the animal body causes, therefore, in this case 

 the appearance of a specific substance able to destroy the carbo- 

 hydrate. The lactase may be called an antibody. If we inject, 

 however, lactose directly into the blood, lactase is not produced. 

 The mechanism of the production of this substance seems to 

 have been in the main cleared up by Bayliss and Starling and 

 Bainbridge. It appears that through the introduction of lactose 

 into the alimentary canal a substance is formed in the mucous 

 membrane of the small intestine, which gradually passes into 

 the circulation and causes the pancreas to secrete the lactase. 

 It is possible to extract this substance from the intestines in 

 vitro and to cause a secretion of lactase by injecting the extract 

 into a vein. In this case it is not the original substance itself 

 which by passing into the circulation causes directly the appear- 

 ance of an antibody, but it is a second substance formed under 



