INTRODUCTION 23 



tion there is no effective resistance on the part of the body 

 cells to the growth and multiplication of the foreign pro- 

 tein. During this time the man is not sick, and we conclude 

 therefore that it is not the growth of the foreign protein 

 which per se gives rise to the symptoms of typhoid fever. 

 However, during this time the body cells are being pre- 

 pared for their combat with the foreign protein. This 

 preparation consists in the development in certain of the 

 body cells of a new function, that of elaborating a new and 

 specific ferment which will digest and destroy the foreign 

 protein. When this new ferment begins its action the 

 first symptoms of the disease appear. The active stage of 

 the disease, with its symptoms and the lesions induced, 

 marks the period over which the parenteral digestion of 

 the foreign protein extends. Death may come from the 

 too rapid breaking up of the foreign protein and the conse- 

 quent liberation of a fatal dose of the protein poison, which 

 is always formed on the disruption of the protein molecule, 

 or it may result from some lesion induced by the products 

 of this disruption, such as perforation and hemorrhage, or 

 it may follow from chronic intoxication and consequent 

 exhaustion. In case of recovery the individual is for a 

 time at least immune to the typhoid bacillus because his 

 body cells are now able to elaborate and make immediately 

 effective the specific ferment which destroys the typhoid 

 protein. 



8. The infectious diseases result from parenteral protein 

 digestion. Parenteral digestion, like all fermentative pro- 

 cesses, is influenced in its rate of progress by many condi- 

 tions, among which may be mentioned the relation between 

 amount of ferment and substrate, the physical condition 

 of the substrate, and the presence of the fermentation 

 products. These influences upon parenteral digestion are 

 not easily ascertained, and consequently not as yet measur- 

 able or controllable. The liberation of heat as measured by 

 body temperature has recently received attention, and we 

 can say in a general way that fever is one of the most easily 

 recognizable effects of the process. While natural infec- 



