ELEMENTARY PHYSIOLOGICAL CHEMISTRY 215 



example of the former is yeast. When this grows in a solution of 

 dextrose it splits the dextrose into alcohol and carbonic acid : 



C 6 H 12 6 = 2C 2 H 5 OH + 2C0 2 . 



An example of the latter is the ferment present in saliva, namely, 

 ptyalin. This resolves polysaccharides into monosaccharides : 



In the case of yeast, the chemical process goes on in the body of the 

 cell, and the energy which is liberated by the splitting up of the 

 complex molecule into simpler ones is used up in the life of the plant. 

 The agent which causes this process is not, however, the vital activity 

 of the yeast cell, but it is an unorganised ferment, called a zymase, 

 manufactured by its protoplasm. If yeast-cells be killed by grinding 

 them in a mortar with sand, and then be subjected to a pressure of 

 500 atmospheres, a clear golden fluid is expressed from them, which, if 

 added to a solution of sugar, produces alcoholic fermentation. We see, 

 therefore, that there is no actual difference between the two kinds of 

 ferments, the organised or living cell ferment owing its properties to 

 an internal secretion in the meshes of its protoplasm. In connection 

 with their conditions of activity there are, however, certain points of 

 difference between unorganised and organised ferments, and especially 

 with regard to the temperature at which they are destroyed. All 

 ferments, organised and unorganised, are destroyed at a temperature 

 of 70 C. in the presence of water. If, however, unorganised ferments 

 be dried, they stand a very much higher temperature. 1 Certain 

 chemical substances e.g. chloroform, alcohol, ether, etc. abolish the 

 action of organised, whereas they do not affect unorganised, ferments. 

 These differences are, however, more apparent than real, for it is 

 evident that when the cell, in the case of organised ferments, has been 

 killed by any of these agencies, it will no longer be capable of absorb- 

 ing into its meshes the substance to be fermented ; and although there 

 may be zymase present in these meshes, it is incapable of acting, 

 because it is locked up in the dead protoplasm of the cell body. 



Certain bacteria, such as B. diphtheriae and B. tetani, behave like 

 gland cells, in that they excrete an unorganised ferment, which, when 

 it gains entry into the blood, produces the symptoms of the disease. 

 Thus, if the fluid in which either of these organisms has been grown 

 be filtered free of bacilli and injected into an animal, the character- 

 istic symptoms are produced. There are bacteria, such as B. coli 



1 The spores of certain bacteria can, however, stand a Very high temperature 

 without being destroyed. For example, the spores of the tetanus bacillus can 

 usually withstand boiling for five minutes. 



