252 MICRO-ORGANISMS AND DISEASE. [CH. xix. 



the lungs, which in severe cases are enormously affected, 

 sometimes only very few of the pathogenic organisms can 

 be discovered. It follows then that the pathological con- 

 dition brought about by the organisms is not due to the 

 direct action of their numbers ; but is an indirect sequence, 

 brought about by definite chemical alterations in the blood 

 or tissues, as the case may be. 



In this we may assume two theories as possible ; (a) It is 

 possible that these chemical effects are produced by the 

 presence and growth of the organisms, as truly as in the 

 alcoholic fermentation of sugar the alcohol produced is a 

 result of the presence of the yeast ; this change is only in 

 so far a product of the organism as this, in its multiplication, 

 assimilates some molecules of carbon and hydrogen, which 

 it abstracts from the sugar, and in consequence of which the 

 sugar yields alcohol ; but it is not, as it were, a secretion of 

 the organism, a special ferment, (b) But it is likewise 

 possible that the organism elaborates a special ferment, 

 which, after a certain amount has been produced, sets up the 

 particular pathological changes. From these considerations 

 it follows that the virus cannot be considered independent 

 of the organism ; we cannot assume that the two can have 

 a separate existence ; for, as we have just now shown, 

 the most feasible assumption, and the one borne out by 

 observation, is that owing to the multiplication of the 

 organisms, certain chemical changes are produced in the 

 blood and tissues, or that a special ferment is created, which 

 sets up the anatomical changes characteristic of the particular 

 disease. 



