50 THE AMERICAN MONTHLY [Feb 
In these cases, predisposition is the last factor added. 
The germ is not the all sufficient cause, but is an import- 
ant factor, capable of setting the disease process in motion 
and of influencing it when other factors are present. It 
is only when the relationship is recognized, that the lim- 
itations of the microscopic and clinical evidence in diag- 
nosis can be understood. A germ disease is where the pa- 
tient furnishes the conditions under which a germ can 
multiply and by its presence, or products, disturb the me- 
tabolism of the human cells. When the environment of 
the cells furnishes them with proper conditions, the re- 
sulting metabolism is a condition of health. 
When there is introduced into this environment any- 
thing which depresses or stimulates the metabolism of 
the cells beyond normal limits, the resulting condition is 
called disease. Therefore it is important to understand 
those things which go to make up environment. 
Temperature, food, the products of cell activity—such 
‘as the ductless glands—and poisons of various kinds, are 
factors of environment whose presence or absence may 
cause disease metabolism. The cell, therefore, is the dom- 
inent entity of life. From its environment it receives 
nourishment and the necessary stimulus which causes it 
to absorb, excrete and reproduce its kind. The bacterial 
cell does not differ in these essentials fromthe human cell. 
It is a Jiving entity and its internal metabolism depends 
uponits environment. When the pathogenic germ finds 
in the human body, conditions which permit it to carry on 
its cycle of activity, its presence becomes a factor in the 
environment of the human cells, which causes disease me- 
tabolism. In the study of infectious diseases, it is im- 
‘portant to recognize the individuality of the different 
pathogenic germs. Each is subject to governing laws, as 
definite as those concerning the human being. | 
Each germ by its form and structure and its former en- 
vironment, possesses individual pathogenic power. All 
