CHEMICAL PHYSIOLOGY. 39 



is the complement. The latter is not specific, since it is furnished 

 by the blood of non-immunized animals, but it is nevertheless essential 

 for hemolysis. Ehrlich believes that the immune body has two side 

 groups one which connects with the receptor of the red corpuscles 

 and one which unites with the haptophor group of the complement, 

 and thus renders possible the ferment-like action of the complement 

 on the red corpuscles. Various antibacterial serums which have not 

 been the success in treating disease they were expected to be are probably 

 too poor in complement, though they may contain plenty of the 

 immune body. 



Quite distinct from the bactericidal, globulicidal, and antitoxic 

 properties of blood is its agglutinating action. This is another result 

 of infection with many kinds of bacteria or their toxins. The blood 

 acquires the property of rendering immobile and clumping together 

 the specific bacteria used in the infection. The test applied to the 

 blood in cases of typhoid fever, and generally called Widal's reaction, 

 depends on this fact. 



The substances that produce this effect are called agglutinins. They 

 also are probably proteid-like in nature, but are more resistant to heat 

 than the lysins. Prolonged heating to over 60 C. is necessary to 

 destroy their activity. 



Lastly, we come to a question which more directly appeals to the 

 physiologist than the preceding, because experiments in relation to 

 immunity have furnished us with what has hitherto been lacking, a 

 means of distinguishing human blood from the blood of other animals. 



The discovery was made by Tchistovitch (1899), and his original 

 experiment was as follows : Eabbits, dogs, goats, and guinea-pigs were 

 inoculated with eel-serum, which is toxic: he thereby obtained from 

 these animals an antitoxic serum. But the serum was not only anti- 

 toxic, but produced a precipitate when added to eel-serum, but not 

 when added to the serum of any other animal. In other words, not only 

 has a specific antitoxin been produced, but also a specific precipitin. 

 Numerous observers have since found that this is a general rule 

 throughout the animal kingdom, including man. If, for instance, a 

 rabbit is treated with human blood, the serum ultimately obtained from 

 the rabbit contains a specific precipitin for human blood; that is to 

 say, a precipitate is formed on adding such a rabbit's serum to human 

 blood, but not when added to the blood of any other animal.* The 

 great value of the test is its delicacy : it will detect the specific blood 

 when it is greatly diluted, after it has been dried for weeks, or even 

 when it is mixed with the blood of other animals. 



* There may be slight reaction with the blood of allied animals; for in- 

 stance, with monkey's blood in the case of man. 



