CHAPTER XXIX 



THE GENERAL PRINCIPLES AND MECHANISM 

 OF INFECTION AND IMMUNITY 



Each and every living thing must feed, assimilate and eliminate. 

 Living matter cannot continue in active life without performing these 

 functions. There are certain resting forms in which these functions 

 are, for the time, held in abeyance. Such are, eggs, spores, seeds and 

 reproductive cells. These organisms possess only potential life; they 

 are not in active life. A grain of corn or wheat, or any vegetable 

 seed, contains a germ cell, a store of food and an enzyme. When 

 placed in the ground, under suitable conditions of temperature and 

 moisture, the enzyme begins to split up the stored food, the germ 

 cells begin to utilize the split products and potential life awakens into 

 active life. The revivified germ cell is now able to feed on the con- 

 stituents of the soil, the stalk grows and the grain or seed is repro- 

 duced. The spores of anthrax are only potentially alive and active 

 life begins anew only in the presence of proper nutriment. The 

 granules into which certain other bacteria are changed in the absence 

 of food are further examples of resting forms. Ova, whether those 

 of lower or higher animals, after stimulation by the spermatic cells, 

 and under proper conditions, begin to develop into active life. In all 

 cases life in one form or another is potentially, at least, continuous. 



No thing in active life remains in a condition of equilibrium. It 

 absorbs, assimilates and eliminates. Metabolism is a life function 

 and there can be no active life without it. Indeed, it is metabolism, 

 active and latent, that distinguishes between living and dead matter. 

 When matter becomes endowed with this function, it is no longer 

 dead, but is alive. Nothing in active life can be conceived of as exist- 

 ing alone. It must have food or die. 



The morphologic unit of life is the cell, although the physiologic 

 unit is the molecule or the group of molecules essential to the celL 

 All living things are essentially proteins. The cell may contain carbo- 



