226 MECHANISM OF INFECTION AND IMMUNITY 



continues, especially when the food proteins are altered by bacterial 

 growth. In rare cases of summer diarrhea, casein, but little altered, 

 has been detected in the blood by biologic tests. Bacteria which cause 

 disease by the elaboration of toxins or poisons in foods before they 

 are taken into the body are known as toxicogenic organisms. This term 

 was proposed by me many years ago. 



Body Cells. These live, like the bacterial cells, by means of their 

 enzymes which also are extracellular and intracellular. The former 

 cleave the pabulum properly and the latter fit the blocks into the mole- 

 cules. The feeding cells are not confined to the leukocytes. All the 

 living cells of the body, so long as they are alive, feed. They eat, 

 assimilate and eliminate. In the higher animals, including man, the 

 gross digestion for the whole is done in the alimentary canal. This is 

 known as enteral digestion. The special preparation of food for the 

 cells of the different organs, however, is done by their own specific 

 enzymes and this process is known as parenteral digestion. Moreover, 

 occasionally, proteins in small amounts pass from the alimentary canal 

 into the lymph and blood without complete digestion. Fine bits of 

 organic matter are inhaled and find their way into the system without 

 being subjected to any form of enteral digestion. Finally, and of 

 the greatest importance in the present study, living proteins, known 

 as bacteria, find their way into the tissues. These not only have 

 escaped enteral digestion, but they are capable of growth and multi- 

 plication, and if their development in the body be prevented it must 

 be through parenteral digestion. Whether they are engulfed by phago- 

 cytes or destroyed by the fluids, it is in either case parenteral digestion. 

 It must be evident that parenteral digestion is the big and deciding 

 factor in most cases of infection. If it fails or if it is slow in pro- 

 cedure, the invading bacteria may multiply. If it proceeds promptly 

 and efficiently the invaders, which under natural conditions are few 

 in number, are destroyed before they can multiply and the body is 

 protected. Now, we have the great problem of infection and immunity 

 fairly before us. It is a contest between bacterial and body cells and, 

 as we have seen, they are armed with similar weapons. The bacterial 

 cells have their enzymes, poisons and toxins. The body cells have 

 their enzymes, bactericidal and bacteriolytic agents, opsonins, and 

 phagocytes. The phagocytes constitute the mobile army of defense 



