16 THE BODY AT WORK 



a different kind. They belong to the descending series. Close 

 molecules are unfolded. Water is incorporated with them. 

 Hydrogen and carbon are oxidized into water and carbonic acid. 

 The conversion into sugar of glycogen or of starch may be 

 taken as an illustration of expansion. Starch, (C 6 H 10 5 ) n , 

 becomes maltose, C^H^On, an d then dextrose, C 6 H 12 6 . The 

 grouped molecule of starch opens out. The breaking of the 

 double molecule of maltose into two molecules of dextrose is 

 a further illustration of progress towards simplicity. Hydra- 

 tion, union with H 2 0, accompanies this expansion. Hydrolysis 

 is the secret of almost all digestive acts. Starch is hydrolysed 

 into sugar, fat hydrolysed into glycerin and fatty acid, proteins 

 hydrolysed into peptones. 



All the chemical transformations which protoplasm is able 

 to accomplish are of the nature of fermentations. The term 

 fermentation was first applied to the effervescence which 

 occurs in grape- juice when its sugar is being converted into 

 alcohol, carbonic acid gas, and certain substances which appear 

 in relatively small quantities. It was discovered later that the 

 yeast which effects this change is a unicellular plant. The 

 term " fermentation " was extended to the production of 

 vinegar from alcohol, and eventually to all such reactions as 

 are carried out by living organisms, or by the secretions or 

 products of living organisms, without the destruction of 

 the agent which is effective in the process. A ferment is an 

 organic body which brings about changes in other bodies with- 

 out itself undergoing change. At the end of the process, how- 

 ever prolonged, there is as much ferment as there was at the 

 beginning, and its chemical nature is the same. Rennin has 

 been made to curdle nearly a million times its weight of milk, 

 pepsin to digest half a million times its weight of fibrin. As 

 the ferment is not consumed, there is no relation, except one of 

 speed, between the ferment and the quantity of fermentable 

 substance which it is able to transform. We said that a fer- 

 ment is an organic body. It is necessary to introduce the 

 qualification " organic," because certain reactions termed 

 " catalyses " which occur in mineral chemistry resemble fer- 

 mentations in respect of the non-destruction of the agent which 

 serves as intermediary. If a solution of cane-sugar containing 

 a very small quantity of sulphuric acid is boiled, the cane-sugar 



