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-miUimetres 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 

 baciUus. 



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 efieet, 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 

 30° and 50°. It is probable that this 

 action is due to the presence of an 

 organized ferment (animal or vege- 

 ¥ig.eo.-Ba^iuBamy. table ccUs), which here supplies the 

 ™s"!butyricfermrat place of the microbc of lactic fermen- 



agent in the fabrica- . 



tion of cheese. tatlOD. 



It is with rennet, or with the still more active 

 liquid produced by the maceration of the testicle of an 

 un weaned calf, that those cheeses are made which 

 consist only of curd, boiled or unboiled, fresh or fer- 



