PRESIDENTIAL ADDRESS Xt 



III. Spirilla.- — (is-ic-i7) Include all the curved and spiral 

 fotnis— -Vibrios, &c. 



Bacteria have also been grouped, *'^^' it can scarcely be called 

 classified, according to the changes they effect in the media in 

 which thej grow. 



1. Zymogenetic, or ferment producing. 



2. Pathogenetic, or disease ,, 



3. Saprogenetic, or putrefaction ,, 



4. Chromogenetic, or colour ,, 



5. Photogenetic, or phosphorescence ,, 



Zymogknetic. — To understand the conduct of some of the 

 ferment producing growths it is well to refer to the behaviour of 

 the yeast plant (of which, by the way, there are many), in the 

 well-known domestic processes of baking and brewing. These 

 processes have perhaps been known during all human time — 

 leaven is referred to in the Oldest of Books, and fermented 

 drinks of one kind or another have been quaffed by the most 

 savage races — and yet the scientific causes, the chemical and 

 vital influences at work have only recently been established. 



The Yeasts (19-20-21-22) .^re half-brothers of the Moulds, the 

 thread-like hairy patches which grow on paste, bread, potatoes, 

 &c., and first cousins of the Bacteria. They, under certain 

 restricted conditions, sporulate, but generally they multiply by 

 budding, hence the name " sprouting fungi,' the daughter cell 

 springing from the protoplasm of the parent and then separating 

 and enjoying an independent life. The cells are oval, about .:i,r„,T 

 of an inch in length, and they proliferate so readily, it has been 

 calculated that one solitary cell in 48 hours will be responsible 

 for something over 35,000— -(35,378 Engel). And an important 

 change — fermentation — is taking place in the medium in which 

 this enonjjous growth occurs. Let it be a saccharine one ; the 

 complex substance — sugar — is broken up ; alcohol is produced ;. 

 car])(inic acid gas given ofi' and heat generated. One molecule 

 of grape sugar may be resolved, theoretically, during the act of 

 fermentation into two molecules of alcohol and two molecules of 

 carbon dioxide. '^3' 



Grape Sn^-ar (IHO) Alcohol (2 x 46) Carbon Dioxide (2 x 44) 



^rH,,0^ = 2~{C^,R^) X ^(CO^ 



or roughly, two parts by weight of sugar yield one of alcohol. 



In Baking, something analogous to this — panary ferment- 

 ation — takes place. Given flour or meal ; leaven or yeast ; water 

 containing salt ; with a sul^cient temperature and a sufficient time 



