CHAPTER V 



THE RELATIONS OF BACTERIA TO DISEASE 



AMONG the earliest records of history theories re- 

 garding the causes of disease may be found. The 

 belief that the sick man was possessed of the devil 

 seems to have been the first and most lasting belief, 

 for it is still held by the savage races, and may be 

 found among the ignorant classes of civilized nations, 

 who hold it to be the cause of insanity. 



During the middle ages, when men began to study 

 the structure and composition of the body, the Hip- 

 pocratic theory that the body contained four hu- 

 mors, viz. blood, phlegm, and black and yellow 

 bile, which worked in harmony in health, but lost 

 their proportion in disease, was the generally ac- 

 cepted belief as the cause of disease; but the reasons 

 for the loss of proper proportion were not stated. 



Later many vague speculations, based more upon 

 imagination than upon facts, prevailed, until Pas- 

 teur's investigations into bacteria as a cause for fer- 

 mentations led to his discoveries and proofs that the 

 infectious diseases owed their origin to bacteria. 



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