94 



FERMENTS AND MICRO-PAKASITES. 



The earliest 



<hscovery of 



parasitic ex- 



Hauler's 

 discoveries 



Actual facts in support of the theory of the develop- 



... , . . f- 



ment oi disease by micro-organisms were first ob- 

 tained *>y tn e study of a number of diseases of plants 

 and insects. As far back as 1835 Bassi demonstrated 

 that a fungus was the cause of muscardine, a fatal 

 disease of silkworms ; other diseases of insects were 

 shortly afterwards demonstrated with certainty to be 

 due to similar fungi ; in like manner Tulasne, de Bary, 

 and Kiihn explained a number of devastating diseases 

 of various kinds of grain, of potatoes, &c., by the 

 entrance and parasitic development of fungi. Also in 

 the case of the higher animals and man positive proof 

 was soon obtained that minute vegetable bodies were the 

 cause of certain diseases. Apart from numerous dis- 

 coveries of fungi which could not with certainty be 

 demonstrated to be the cause of the accompanying 

 diseases, favus, thrush, and various affections of the 

 skin were shown to be dependent on parasitic micro- 

 scopic fungi. Of especial importance was the discovery 

 that anthrax was characterised by the appearance in the 

 blood of minute rod-shaped organisms, and that these 

 organisms could be shown experimentally to be the 

 cause of the disease (Pollender, 1855 ; Davaine, 1863). 



On the one hand the constantly increasing frequency 

 of severe pestilences which led to the earnest desire to 

 solve the etiological questions, on the other hand the 

 convincing deductions of Henle, the numerous analogies 

 with diseases of plants and animals, and the discovery 

 of the contagium of anthrax, gave rise to a period of 

 research which was characterised by an excess of zeal 

 and by a large number of imperfectly proved discoveries 

 which were of no real advantage to the parasitic theory. 



It was Hallier more particularly who became a too 

 en thusiastic apostle of the parasitic theory. As the 

 result of numerous researches he asserted that the 

 various micro-organisms only represented special vege- 

 tative forms of known mould fungi, arising in conse- 

 quence of the external conditions of life ; that these 

 vegetative forms gave rise to all sorts of diseases, but 

 that under suitable conditions one could always cultivate 



