148 LEO LOEB. 



at different periods of the day and that these variations indicate 

 a certain relationship to the time at which the food is taken in and 

 at which trypsin is secreted. This is very suggestive of the rapid 

 formation of an antibody in response to the normal increase of 

 a certain ferment in the circulation. In a similar way the blood 

 serum of a horse and a pig was found by Briot, Roden and Kor- 

 schun to contain normally an antibody against rennin. This 

 natural antibody acts in the same way as the one experimentally 

 produced by injecting rennin into other animals, probably com- 

 bining with the rennin. A further observation strengthening the 

 evidence that autoimmunizatory processes may take place is that 

 during the puerperium an increase of isoagglutinins takes place 

 in the human body. This is probably the result of the resorption 

 of substances from the uterus and other organs. The resorption 

 of these substances seems to modify the action of the blood 

 serum on the blood cells of the same species of animals. 



The specific character of the experimentally produced anti- 

 bodies is quite marked ; these antibodies possess a certain rela- 

 tionship to that substance whose introduction into the animal 

 organism caused the antibody to appear. This specificity is of a 

 twofold character. In the first place the antibody reacts only 

 against a chemical substance similar in composition to the one 

 which caused it to originate, secondly there exists a species 

 specificity. Substances apparently equally constituted, but de- 

 rived from different species, behave differently towards the anti- 

 body, those substances showing the strongest reaction which are 

 derived from the same species, or from a species similar to the 

 one from which the substance was obtained whose introduction 

 into an animal organism caused the formation of the antibody. 

 The latter (and also the former) kind of specificity is not abso- 

 lute, substances derived from nearly related species showing a 

 similar although usually a weaker reaction. 



Such a specificity may also be noticed in the adaptations de- 

 scribed above. The snake and scorpion antitoxin are specific for 

 snake and scorpion toxin respectively. The leech extract is 

 without effect on the plasma of invertebrates, but acts only on 

 the plasma of vertebrates ; in the case of ixodes and anchylo- 

 stoma, the specificity may perhaps even go farther, so that the 



