GENERAL PROPERTIES OF THE FERMENTS. 113 



of water likewise inhibits the action of the ferments, but this is at 

 once re-established when the necessary degree of moisture is supplied, 

 and it is possible therefore to preserve the ferments in the dry state. 

 During the process of drying, however, care must be had that the 

 temperature does not exceed a certain limit. This varies with the 

 different ferments, but it may be stated as a general rule that all 

 animal ferments are killed by a temperature of 75 C., while the 

 vegetable ferments cannot survive a temperature of 80 C. In the 

 absence of moisture, however, they can apparently withstand much 

 greater heat, and it is said that dry trypsin, pepsin, and diastase 

 may be heated to a temperature of from 150 to 160 C. without 

 losing their activity. Strong alcohol destroys the action of certain 

 ferments, such as pepsin and diastase, while others, like the fibrin- 

 ferment, are not affected unless the contact is prolonged. 



A most peculiar property of the ferments, and one which is char- 

 acteristic of all, is the power to bring about an amount of chemical 

 change which is apparently out of all proportion to the quantity of 

 the ferment present, while the ferment itself undergoes no apparent 

 change. The common pepsin preparations of the market are of 

 a strength that 1 part by weight of the pepsin will digest 6000 

 parts by weight of coagulated egg-albumin, and Petit claims that 

 a preparation from his laboratory was capable of dissolving even 

 500,000 times its weight of fibrin in seven hours. Invertase has 

 been shown capable of inverting 200,000 times its own weight of 

 cane-sugar, and rennin at least 400,000 times its own amount of 

 casein. 



That the ferments themselves undergo no change while exerting 

 their specific action can be readily shown, as it is possible to reobtain 

 them from the various digestive mixtures and to test their efficacy 

 as before. It is to be noted, however, that this is impaired to a 

 certain extent, but such impairment is referable to loss of ferment, 

 and not due to the reaction. It has been rendered quite probable 

 that during ferment action the ferment, temporarily at least, enters 

 into combination with the substance to which it is " tuned." 



The rapidity with which the action of ferments takes place is often 

 most remarkable, and is especially well shown during the coagula- 

 tion of milk under the influence of rennin. 



In order that the ferments may exhibit their activity to best 

 advantage a definite temperature is necessary, which varies some- 

 what with the different ferments, but is generally about that of the 

 body. Higher as well as lower temperatures gradually inhibit their 

 action, and, as has been seen, destroy it entirely when 75-80 C. is 

 reached. Very low temperature has the same effect. 



Oxygen has no effect upon the action of most ferments, and they 

 thus show a distinct difference from the organized ferments, which 

 are more or less dependent upon its presence or its absence. 



The reaction of the medium in which the ferments are to display 

 their activity is very important, and varies with the different fer- 

 8 



