HISTORICAL INTRODUCTION. 7 



causal connection was established between these organisms and the 

 disease ; and when the cholera disappeared the interest in contagium 

 rim HI \vaiied, and was eclipsed by the question of fermentation. 

 The discoveries which followed in this subject had a very important 

 1) :aring on the micro-parasitic origin of communicable diseases. 



Pasteur, following up the researches of Cagniard Latour and 

 Schwann, demonstrated in 1857 that the lactic, acetic, and butyric 

 fermentations were produced by micro-organisms. 



Previously to this, in 1850, Davaiiie and Rayer had noted the 

 existence of little rod-like or filamentous bodies about the size of a 

 blood corpuscle in the blood of a sheep that had cjiecl of splenic fever. 

 Pollender had seen similar bodies in the blood of cows. Davaine 

 did not at first pay much heed to this discovery; but in 1863 he 

 thoroughly reinvestigated the subject, and conducted a series of 

 experiments which led him to the conclusion that the actual cause 

 of splenic fever was an organised being whose presence and 

 multiplication in the blood produced changes in that fluid of the 

 nature of fermentation, resulting in the death of the animal. 



These conclusions were not accepted by all, and indeed, the 

 evidence was so far incomplete that sceptics were justified in con- 

 sidering that these experiments afforded only a working hypothesis. 

 But Davaine's comparison between this disease and fermentation 

 attracted the attention of Pasteur, whose mind had been fully trained 

 for entering upon this investigation by the researches which he had 

 been carrying on in the interval between Davaine's publications of 

 1857 and 1863. 



Pasteur, as already mentioned, had been working at fermentation, 

 and his attention was next directed to studying the so-called diseases 

 of wines, and subsequently to a contagious disease which committed 

 ravages among silkworms. By laborious researches Pasteur was 

 able to confirm the belief that this disease of silkworms was due to 

 the presence of micro-organisms discernible with the aid of the micro- 

 scope. These oval shining bodies in the moth, worm, and eggs had 

 been previously observed by Cornalia, and described by Nageli as 

 Nosema bombycis, and by Lebert as Panhistophyton. But it was 

 reserved for Pasteur to introduce a means of combating the disease. 

 Pasteur showed that when a silkworm, whose body contained these 

 micro-organisms, was pounded up with water in a mortar, and the 

 mixture painted with a brush on the leaves on which healthy w r orms 

 were fed, they would all without fail succumb to the disease. 



As the contagious particles were transmitted to the eggs, a 

 method for preventing the spread of the disease suggested itself. 



