FERMENTS AND MICRO-PARASITES. 



once destroyed when the yeast cells die, or even when 

 their life is interfered with. 



As the result of the preceding historical sketch of the 

 development of the views on fermentation and putrefac- 

 tion, we may take it as absolutely certain that minute 

 living organisms are the direct cause of the processes 

 commonly grouped together under these terms, and 

 that these processes are intimately dependent on the life 

 of the organisms. 



II. MICRO-ORGANISMS AS PARASITIC EXCITING AGENTS 

 OF DISEASE. 



Even at an early period of scientific observation and 

 research on the subject of the infective diseases, we meet 

 with the belief that the immediate cause of these de- 

 vastating affections is an entity endowed with vital 

 Earlier hypo- properties, a contagium animatum. This view was 

 the organised clearly expressed by Hufeland ; but at first all sorts of 

 fantastic notions as to the more intimate nature and 

 mode of action of this supposed entity, endowed with 

 vital properties, were added to these leading ideas. Soon, 

 however, there was evolved from this cloud of phantasies 

 the definite view that the transmission of the infective 

 diseases depended on the growth of independent minute 

 organisms (Kircher, Linne, Wichmann, and others). In 

 fact it was extremely tempting to refer the characteristic 

 phenomena in the occurrence of the infective diseases to 

 such organisms, and to draw a certain parallel between 

 these diseases and the processes of fermentation and 

 putrefaction, which are likewise caused by similar fungi. 

 The sudden appearance of epidemics in various isolated 

 places, their relatively slow spread, and the fact that 

 they often remain localised to a particular locality, must 

 exclude the idea of an evanescent, gaseous agent. The 

 mode of their spread, the unlimited development of the 

 infective material through a large series of individuals, 

 the transport of the infective material over considerable 

 distances, its adherence to the most heterogeneous ob- 

 jects, the stage of incubation, the typical cyclical course 



