400 
Micro-organisms and their Action 
various circumstances. As to all the decompositions the butter- 
fat contained in the cheese is able to undergo, our knowledge is 
also far from complete. Moreover, smell and taste are so much 
more sensitive than all our chemical re-agents, that the quantities 
of products of certain fermentative actions may be quite large 
enough to give the cheese in which they are present a distinct 
character, and yet be far too small to allow of their chemical 
recognition, definition, and quantitative determination. 
Considerins: this, and bearins: in mind that the studv of 
micro-organisms and their action is still in its infancy, much 
definite knowledge can scarcely be expected. The most im- 
portant systematic investigation on the subject is that made by 
^I. Duclaux on the manufacture and ripening of Cantal cheese. 
This cheese is said to contain ten or more micro-organisms, of 
which six are supposed to be of especial importance. There is 
an alcoholic ferment, a lactic ferment, a butyric ferment, and a 
ferment acting upon the casein and forming alkaline nitrogenous 
compounds of simple composition. These four ferments have to 
perform well-defined functions, but of the greatest importance 
are the remaining two. 
The one is described as a vibrio forming chains, which 
exhibit an undulating motion ; the vibrio prefers a temperature 
of 75' to %y Fahr., and forms spores. When introduced into 
milk the vibrio causes the development of carbonic acid and 
hydrogen gas. Sugar and fat are not acted upon, but casein 
is transformed into an albuminous substance soluble in water, 
even in the presence of acid. At the same time small quanti- 
ties of butyric acid and ammonium butyrate are produced. 
When in the manufacture of the cheese the curd is cut up 
in order to get rid of the whey, the vibrio causes the parts of 
the coagulum to stick together and form a solid mass of cheese ; 
the presence of the ferment is therefore desired in the whey. 
If, however, it enters into the coagulum itself, it will give 
rise to the formation of gas which heaves the cheese, and also 
butyric acid and its compounds, which will spoil the taste. 
The vibrio resists a temperature of 170^ Fahr. ; the spores 
resist a temperature even above boiling-point. 
The other ferment is a bacillus, growing in the shape of thin 
threads on the surface of liquids, and shorter and thicker if sub- 
merged. Like the previously described ferment, it acts upon 
the casein, transforming it into a soluble substance, which is 
neither precipitated by acids nor coagulated by boiling. Besides 
this nitrogenous body acetic acid is formed, as well as a sub- 
stance of an intensely bitter taste, which makes the ferment 
highly objectionable. As this bacillus resists the temperature 
of boiling water, its destruction is a matter of considerable 
difficulty. 
