20 VACCINE AND SERUM THERAPY. 



obtained. It seems quite definite that in certain cases, internal 

 organs may contain more immune substances than the blood se- 

 rum. After immune bodies have been formed they do not remain 

 permanently in the body, but are gradually lost through destruc- 

 tion in the body or lost with the excretions. 



Ehrlich's views on the formation of immune bodies are quite 

 generally accepted. His views, however, concerning the com- 

 bination of toxin and anti-toxin, agglutinable substances and 

 agglutinins, and substances capable of solution and lysins are 

 not as universally accepted. Ehrlich assumes that the union of 

 immune bodies and the specific substances is a chemical combina- 

 tion. Bordet assumes that in lytic sera the immune body acts 

 as a mordant which sensitizes the substance capable of solution 

 to the action of the complement. Field has explained the inter- 

 action of immune bodies and specific substance according to the 

 principles of colloid chemistry, so that for example in a toxin 

 and anti-toxin combination one is adsorbed (physical rather than 

 chemical) by the other. 



OPSONIN THEORY OF IMMUNITY. 



It has been stated earlier that in 1883, Metchnikoff advanced 

 his phagocytic theory of immunity. According to this theory 

 the presence or absence of immunity depends upon the, ability of 

 phagocytes to engulf and destroy bacteria. Metchnikoff had 

 given serum little consideration in immunity although he believed 

 that some sera contain substances which stimulate the leucocytes 

 to engulf bacteria. These substances he called "stmiulins." The 

 phagocytic theory, however, was practically replaced by the 

 humeral theory of immunity because Fudor, Buchner, Behring, 

 Nuttall and others had found that serum containing no cells 

 whatever can destroy bacteria by solution. It was also found 

 that antitoxin, which combines with toxin, is carried in serum. 



From 1887 on the humeral theory of immunity gained a 

 strong foothold and it was not until 1895 that attention was again 

 called to the function of the leucocytes in immunity. In this 

 year Denys and LeClef reported experiments from which they 

 concluded that in immunization certian changes are produced 

 in the serum, which make it possible for the leucocytes to engulf 

 bacteria. In their conclusions they state that leucocytes from a 



