THE CHEMICAL BASIS OF THE BODY 763 



Very little is known of the process of fermentation. The first 

 important addition to a knowledge of the subject was the discovery 

 of the above fact, that a ferment may be either living or non-living 

 matter— or, as it is termed, organised and unorganised — and that 

 no essential difference exists between them, as the living ferment 

 acts by producing within itself an enzyme which does the work. 

 It is by means of^enzymes or ferments that all the striking phenomena 

 connected with the processes of digestion are carried out. None 

 of the food substances taken into the alimentary canal are capable 

 of absorption excepting through their agency, so that the impor- 

 tance of a study of fermentation in this connection alone is of the 

 greatest interest ; the part played by ferments in the liver, in the 

 clotting of blood and milk, and the formation of ammonia from 

 urea, has been previously pointed out. 



The explanation of fermentative processes is considered to be due 

 to catalysis, or a reaction induced by the presence or contact of 

 another substance, called a catalyser, which takes no part in the 

 reaction. Such bodies are known in inorganic chemistry — for ex- 

 ample, the union of oxygen and hydrogen at ordinary tempera- 

 tures to form water is induced by the presence of spongy platinum, 

 which in itself undergoes no change, but by its presence accelerates 

 the rapidity with which the union occurs, or, as the chemist expresses 

 it, the velocity of reaction. In organic chemistry a good example 

 of catalytic action is furnished by the change induced in a solution 

 of cane-sugar in water. Under ordinary circumstances this is very 

 slowly converted into equal quantities of kevulose and dextrose, 

 but the addition of a little mineral acid effects it in a few minutes. 

 The action of the acid is to increase the velocity of reaction. It 

 is reasonable to suppose that the enzymes of the body and ferments 

 generally act like the catalysers : they effect profound changes in 

 the bodies with which they come into contact, but undergo no change 

 themselves ; and it may further be added that a very small quantity 

 is capable, under suitable conditions, of acting indefinitely. 



In order, however, that a ferment may act indefinitely, it is neces- 

 sary that the products of its activity be removed as formed, as they 

 are in the intestinal canal by absorption. An accumulation of the 

 products stops the reaction ; but if these be removed, the process 

 recommences. The arrest of fermentation by the accumulation 

 of its own products is shown in some enzymes to be due to what is 

 called a reversible action ; the catalyser, in presence of the now ex- 

 cessive mass of the products of its own activity, effects a process of 

 reconstruction into the original substances. This was first shown 

 by the action of maltase — a ferment contained both in yeast and the 

 intestinal juice — on maltose, which it converts into dextrose, though 

 under suitable conditions it reconstructs a small quantity of maltose 

 from dextrose. Similarly, as was pointed out at p. 256, the fats in 

 the intestinal canal are acted upon by lipase, broken up, and ren- 

 dered soluble. In the tissues lipase causes a reconstruction of fat. 

 Under conditions where fat is lost to the body, it is lipase which 

 splits it up and renders it capable of being oxidised as focd. 



The chemical action of nearly all body ferments is hydrolytic — 

 i.e., the substance acted upon takes up the elements of water, and 

 splits into simpler bodies. 



The activity of ferments is influenced by temperature. At 

 freezing - point they are inactive for all ferments employed ty 

 warm-blooded animals. At 65 C. (149 F.) all body ferments are 



