580 BACTERIOLOGY. 



typical cases of typhoid fever, for instance, that termi- 

 nate fatally, and that have exhibited little or no clinical 

 signs of resistance at any time during their course. 



Fifth, there may be demonstrated in the blood of 

 animals that have received repeated subcutaneous injec- 

 tions of milk a body a "precipitin" that causes a 

 precipitation of milk. This precipitation represents 

 apparently a specific reaction, for it occurs only when 

 the blood-serum is mixed with milk from the species of 

 animal that supplied the milk used for the injections. 



Sixth, after the repeated injection of blood or of 

 emulsions of tissue-cells into the body of an animal, 

 there appear in the blood of that animal certain solvents, 

 or enzyme-like bodies, " hsemolysins," " cytolysins," etc., 

 that react specifically upon the blood or tissue-cells in- 

 jected, agglutinating, disintegrating, and finally com- 

 pletely dissolving them. Here, too, the relations are 

 specific. If a rabbit, for instance, be rendered tolerant 

 to or immune from beef-blood, its serum dissolves only 

 the red corpuscles of bo vines; if from dog's blood, then 

 only the corpuscles of the dog are dissolved by the 

 serum of the rabbit. Similarly, if a rabbit be rendered 

 tolerant to injections of emulsions of epithelium cells, 

 then its serum dissolves epithelium and not necessarily 

 other cells. All these reactions may be seen in a test- 

 tube or under the microscope. 



Seventh, if a hsernolyzing serum, prepared as indi- 

 cated under the sixth observation, be heated for a short 

 time to 54-56C., it at once loses the hsemolytic func- 

 tion, but regains it again if a few drops of serum from 

 a normal animal be added to it. In this phenomenon 

 pf haemolysis Ehrlich's "receptors of the third order" 



