INFECTION AND 1MMI)NITY. 575 



only the corpuscles of the dog arc 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 other cells. 

 All these reactions may be seen in a test-tube or under 

 the microscope. Seventh, if a hsemolyzing serum, pre- 

 pared as indicated under the sixth observation, be heaterl 

 for a short time to 54°-56° C, it at once loses the 

 hsemolytic function, but regains it again if a few drops 

 of serum from a normal animal be added to it. In this 

 pheuomenon of haemolysis Ehrlich's "I'eeeptors of the 

 third order " are assumed to be concerned ; the heating 

 kills the "complement," and thereby checks the process; 

 but the subsequent addition of the normal serum sup- 

 plies fresh "complement," and at once restores the 

 activity of the hsemolyzing receptors. Eighth, if blood 

 containing a hsemolysin or a cytolysin be repeatedly 

 injected into an animal, anti-bodies — "antilysins" — are 

 formed, and the serum of the animal has the power of 

 robbing a hsemolytic serum of its haemolyzing function 

 if mixed with it in a test-tube.^ 



' It is evident, from what has been said, that the belief in a vital 

 germicidal function possessed by the iluids and tissues of the body is 

 widespread ; is based upon the best of experimental evidence ; and has 

 served as the starting-point for all the important investigations that 

 have been instrumental in moulding our present ideas of immunity. 

 Notwithstanding this, one occasionally encounters a dissenter. Only 

 recently Baumgarten, in an address before the German Pathological 

 Society at Munich (see Berliner kliuische Wochenschrift, 1899, No. 41), 

 made a vigorous attack upon the evidence that has been presented in 

 favor of a vital germicidal function of the blood-serum. He believes 

 the destruction of bacteria observed when they are mixed with blood- 

 serum to be due less to vital than' to physical causes. He regards the 

 death of the organisms in fresh serum as the result of disturbances of 

 assimilation and osmosis, consequent upon their sudden transference 

 from the culture-medium, on which they tave been accustomed to 



