RENNET AND ITS PROPERTIES. 203 



The action of unorganized, or chemical or soluble (hydrolytic) ferments, is 

 believed to take place in such a way that a molecule of the ferment unites 

 with a molecule of the transformed body, and forms a compound which is 

 immediately decomposed by water again. The molecule of the ferment 

 separates out unchanged, and bodies are formed which owe their origin to 

 the hydration of the body undergoing fermentation. It may be supposed 

 that the budding fungi and bacteria act indirectly in exactly the same 

 manner, if it be assumed that they possess the capacity to separate out 

 under certain conditions unorganized ferments or enzymes. 



108. Rennet and its Properties. By the term "rennet" in dairy- 

 ing, is understood the liquid or powdered preparations, suited for 

 purposes of cheese manufacture, which contain as their chief 

 constituent that characteristic rennet ferment which exerts an 

 extraordinarily powerful action on the caseous matter of the milk. 

 This ferment is found in the stomach of a large number of animals, 

 and also in the human stomach. It is especially abundant in the 

 stomach of young mammals while they are still suckling; and is a 

 secretion of the rennet-glands, which are embedded in the lining of 

 the stomach. For the preparation of rennet, calves' stomachs are 

 almost exclusively used, on account of the ease with which they are 

 procured. Up till now it has not been possible to obtain the rennet 

 ferment in a pure condition. From an extract, obtained by treat- 

 ing the dry stomach of a calf with a 5-per-cent salt solution, and 

 then by increasing the percentage of salt to 10 per cent, Soldner 

 obtained a precipitate which, when dried, formed a gray-brown 

 powder. One part of this powder was sufficient to coagulate at 

 35 C., in 40 minutes, one million parts of milk. As the powder 

 contained 36 per cent of organic matter, one part of this was 

 sufficient, therefore, under the above conditions, to effect the 

 coagulation of 2*8 million parts of milk. Further, as the organic 

 substance did not consist of pure rennet, the ferment must there- 

 fore exert a much stronger action on milk. The rennet ferment 

 belongs to the unorganized class of ferments, and more parti- 

 cularly to those which are able to decompose albuminoids. Its 

 action is connected with well-defined conditions, which can be 

 accurately and shortly described. Its action does not take place at 

 all if the milk lack soluble lime salts, and if the milk possess an 

 alkaline reaction, however faint. Milk which colours, or which 

 reddens phenol-pthalein perceptibly, is not coagulated by rennet. 

 An acid reaction, within certain narrow limits, assists the action of 



