lot) GENERAL PHYSIOLOGY 



eiiium, the molecules of the metals undergoing no change. These 

 facts are explained as follows : It is known that accordingto the 

 mechanical theory of heat the atoms in every molecule are in con- 

 stant vibratory motion — a phenomenon that is termed intra- 

 molecular heat. Upon contact of the molecule of the metals in 

 question with the complex molecule of formic acid this intra- 

 molecular vibration of the atoms of the former is transferred to the 

 latter, and combines with the latter 's vibration in such a way that 

 another arrangement of atoms results — i.e., a decomposition of the 

 formic acid molecule. According to a different idea, it is the chem- 

 ical afSnity between the atoms of the molecule of the metal and 

 certain atoms of the formic acid molecule that disturbs the intra- 

 molecular vibrations of the formic acid atoms in such a way that a 

 rearrangement, i.e., a decomposition, takes place, without, however, 

 the occurrence of a real combination of the atoms of the metal 

 with the corresponding atoms of formic acid. However it be, in 

 every case the intramolecular motion of the atoms in the molecules 

 that are to be broken up becomes disturbed, while the catalytic 

 molecule of the metal remains intact. Such contact-actions are 

 widely known in chemistry. Thus, hydrogen peroxide upon 

 contact with finely divided platinum is changed into water and oxy- 

 gen without the platinum itself being altered. 



In contrast to these pure contact-effects, chemistry recog- 

 nises other cases in which the effective body remains unchanged 

 only apparently. While bringing about transformations, it is 

 continually altered chemically, but is immediately re-formed again. 

 The end-results in the two cases must be the same, for even in the 

 latter case at the conclusion the body in question is found in its 

 original form. We have already become -acquainted elsewhere 

 with such a case. In the manufacture of concentrated sulphuric 

 acid the nitric acid is continually reduced by sulphurous anhj'dride 

 into nitrous acid, to be re-formed again into nitric acid with the 

 aid of the oxygen of the air. 



Which of the two cases does the action of ferments resemble ? 

 Thus far this question has not been decided with certainty. It is 

 very probable, however, that among so-called ferment-actions both 

 cases are present. 



In the large group of ferments two kinds are distinguished — dis- 

 solved unorganised ferments, or eii:t/mcs, and solid organised ferments, 

 or ferment-organisms ; the former comprise secretions which are 

 given off to the outside by the living cell and remain constantly 

 effective, the latter consist of the living substance of the cell itself, 

 with the life of which the ferment-action is associated. While 

 in ferment-organisms the ferment-action is extinguished with 

 the life of the cell, the enzymes can be preserved as long as 

 desired as chemical bodies, without losing their power. The cells 

 of yeast (Saeeharnmyccf:), which cause the alcoholic fermentation 



