110 MICROBES, FERMENTS, AND MOULDS. 
Pasteur has ascertained that this fermentation 
results from the development of a microbe which 
takes the form of minute cylindrical rods, rounded at 
their extremities, usually straight, and either isolated 
or united in chains of two or more articulations. 
These rods are about two micro-millimetres in width, 
and from two to twenty micro-millimetres in length. 
They advance with a gliding motion, are often curved, 
and present slight undulations. They are reproduced 
by fission. These characters are those of the genus 
bacillus. 
Coagulation of Milk: Cheese.—The coagulation of 
milk is artificially produced by rennet, the liquid 
secreted in a calf’s stomach. Human gastric juice 
produces the same effect, and the milk introduced as 
an aliment into the stomach is never digested until it 
has been curdled, both in children and adults. The 
artichoke flower, and other plants of the genus Car- 
duus, will also curdle milk at a temperature between 
SS 30° and 50°. It is probable that this 
= Xe action is due to the presence of an 
Ss organized ferment (animal or vege- 
Fig. 60.—Bacitlus amy. table cells), which here supplies the 
ibact butyrt- . . 
aah baie ferment, place of the microbe of lactic fermen- 
eich tation. 
It is with rennet, or with the still more active 
liquid produced by the maceration of the testicle of an 
unweaned calf, that those cheeses are made which 
consist only of curd, boiled or unboiled, fresh or fer- 
