INFECTION AND IMMUNITY. 41 7 



but in some cases must be looked upon more as an anti- 

 dote to their poisonous products. 



6. That in the serum of the normal circulating blood 

 of many animals there exists a substance that is capable, 

 outside of the body, of rendering inert bacteria that, 

 if introduced into the body of the animal, would prove 

 infective. 



7. That phagocytosis, though frequently observed, is 

 not essential to the establishment of immunity, but is 

 more probably a secondary process, the bacteria being 

 taken up by the leucocytes only after having been 

 modified in virulence through the normal germicidal 

 activity of the serum of the blood and of other fluids in 

 the body. 



8. That, of the hypotheses that exist for the explan- 

 ation of immunity, the one which assumes acquired 

 immunity to be due to reactive changes on the part of 

 the tissues has received the greatest support. 



