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Yeast and other Ferments. 

 By C. A. Watkins. 



{Read March 23rd, 1867. j 



In this paper I shall endeavour to lay before you some of those 

 chemical changes which take place in certain substances when under 

 the influence of other substances called Ferments. In some of 

 these transformations the microscope shews us that there exists an 

 intimate connection between the processes and the growth of some 

 minute organisms, while in others the changes are purely chemical. 

 The subject, which is of interest alike to the physiologist, micro- 

 scopist, and chemist, has received great attention from many ex- 

 cellent observers ; nevertheless, very little is known about it, and 

 at present the whole matter is involved in great mystery. 



I, therefore, feel considerable diffidence in addressing you on such 

 a subject, and should not have attempted it had I not observed that 

 many writers fall into serious errors when discussing the chemical 

 operations of the Ferments. 



I may at once tell you that the matter contained in this paper is 

 perhaps more chemical than microscopical ; but the fact is, these 

 two investigations are inseparable if we desire accurate knowledge, 

 and it is impossible to view Ferments broadly, if treated only as a 

 chemical or only as a microscopical subject. 



Fermentation is a term applied to various chemical transforma- 

 tions, which certain ordinarily stable compounds, such as starch and 

 sugar, undergo when in contact with a small quantity of an azotised 

 or albuminous substance, which is itself in an active state of altera- 

 tion. This active substance is called a Ferment, and one of the 

 peculiar properties of such a body is that it receives nothing from, 

 nor imparts anything to, the matter which is undergoing fermenta- 

 tion, but is itself decomposed and destroyed as a Ferment in pro- 

 portion to the matter fermented, which is gradually split up, or un- 

 folded into two or more substances of simpler composition, some- 

 times with and sometimes without the assimilation of water. 



Journ. Q. M. C. No. 13. m 



