5io A MANUAL OF PHYSIOLOGY 



yeast-cells, and bacteria possess such ferments, but their existence 

 has been demonstrated in practically all the organs of the higher 

 animals and man. When a piece of liver, e.g., is removed with 

 aseptic precautions and kept at body-temperature, extensive 

 auto-digestion occurs, and ammonia, and other basic substances, 

 glycin, and the body which gives the tryptophane reaction 

 (p. 430), appear among the products. Tyrosin appears so early 

 that it is scarcely possible to doubt that it must be a product 

 of protein decomposition in the liver-cells under normal con- 

 ditions. Similar autolytic processes have been observed in the 

 spleen, muscle, lymph-glands, kidneys, lungs, stomach wall 

 (independently of pepsin), thymus, and placenta, also in patho- 

 logical new growths like carcinoma, in the breaking down of 

 which and in the removal of such exudations as occur in the 

 alveoli in pneumonia, these proteolytic ferments seem to play a 

 part. The ferments in certain cases have been obtained in 

 extracts of the organs, and have been found still active. It is 

 probable that the syntheses of the proteins or their products, 

 which are scarcely less characteristic of the tissue cells than 

 the decompositions effected by them, are also due to the 

 action of separate intracellular ferments or upon the reversed 

 activity of the proteolytic ferments. So many of the chemical 

 reactions of the body have been found to depend upon enzymes 

 that modern physiology may at first thought seem almost to 

 have reverted to the position of van Helmont and his school in 

 the seventeenth century, who resolved all difficulties by murmur- 

 ing the magic word ' ferment.' No fewer than eleven ferments 

 have been stated to be present and active in the liver alone 

 viz., a proteolytic and a nuclein-splitting ferment, a ferment 

 which splits off ammonia from amino-acids, a milk-curdling 

 ferment, a fibrin ferment, a bactericidal ferment, an oxydase, a 

 lipase, a maltase, a ferment called glycogenase, which changes 

 glycogen into dextrose, and an autolytic ferment. In the 

 presence of such an array of enzymes the organs might seem to 

 be little more than incubators in which the ferments do their 

 work. It must not be supposed, however, that the intracellular 

 ferments, whether they cause decomposition or synthesis, 

 oxidation or reduction, work independently of what, for want of a 

 better name, we must call the organization of the cell. We may 

 be sure they are the servants and not the masters of the proto- 

 plasm, and that a drop of an extract containing intracellular 

 ferments has very different powers from a living cell. ' It is not 

 in the existence of the ferments, but in their combined action at 

 the proper time and in the proper intensity, that the riddle of 

 metabolism lies ' (Hober). 



2. Metabolism of Carbo-hydrates Glycogen. The carbo- 



