22 PROTEIN POISONS 



the proteins of the body. All living cells grow by means 

 of their own digestive ferments, and these must act upon 

 the pabulum within their reach. If the ferment of the 

 bacterial cell cannot digest and prepare food for the bac- 

 terium from the body proteins, then the invading bacterial 

 cell dies. The second factor in determining whether a 

 given bacterial cell will grow in the animal body is the 

 effect of the ferments of the body cells on the invader. If 

 these are rapidly and thoroughly destructive there is no 

 bacterial development, and the organism is innocuous. 

 The prodigiosus is not pathogenic, but the cellular sub- 

 stance of this bacillus obtained by growth on artificial culture 

 media is highly poisonous to animals. This is true, with 

 modification as to degree, of the cellular substance of all 

 non-pathogenic bacteria. It is not the lack of poison in 

 the substance when placed under conditions favorable to 

 its growth, but it is its inability to grow under unfavorable 

 conditions. The smallpox virus is pathogenic to the unvac- 

 cinated but non-pathogenic to the vaccinated, because by 

 vaccination there has been developed in the body a ferment 

 which destroys the smallpox virus before it can develop. 



7. Any foreign protein which can grow and multiply in the 

 body of a given animal may prove pathogenic to that animal. 

 Our idea of the development of an infectious disease may 

 be stated as follows: An infective agent is any protein 

 which possesses the capability of growth in the animal 

 body. What these essentials are have been stated under 6. 

 We will take as illustration typhoid fever. The infective 

 agent is the typhoid bacillus, a specific, particulate protein. 

 It is infective because by means of its digestive ferment it 

 can feed upon the proteins of man's body. This means 

 that it can convert man's proteins into typhoid proteins 

 and thus multiply its kind. Moreover, it is not, imme- 

 diately on its entrance in man's body, destroyed by the 

 ferments of the body cells. Having found admission to the 

 body it proceeds to grow and multiply. This continues 

 through the period of incubation, which in this disease is 

 somewhere about ten days. During this period of incuba- 



