The Living Machine 295 



and various vegetable oils can be burned in a lamp. When 

 taken into the digestive tract however the fat is not usable 

 as fuel any more than any other food substance, but must 

 first undergo digestion. 



The function of digestion of all food is to put it into such 

 shape that it can be absorbed by the blood and lymph through 

 the walls of the digestive tract. This transfer or absorption 

 of the food through the latter takes place, as we have seen, 

 by a process of osmosis. The food as eaten is not ordinarily 

 in solution and cannot be passed through a membrane or 

 dialyzed, the function of digestion being to render it soluble 

 and dialyzable. This is accomplished by a process known as 

 hydrolysis which consists in the splitting up of the food into 

 simpler compounds by the addition of water. This process 

 is effected by means of certain remarkable substances formed 

 by all animals and plants and known as enzymes or ferments. 

 When a little yeast is added to a solution of sugar and certain 

 salts and kept at a proper temperature, bubbles of gas (carbon 

 dioxide) soon begin to rise to the surface of the solution. 

 The sugar is being broken down into two simpler substances, 

 carbon- dioxide and alcohol, by the ferment secreted by the 

 yeast cells. So far as we know the ferment itself does not 

 change, but acting as by magic affects a change in certain 

 substances with which it comes in contact. Yet even this 

 remarkable activity of the living cell has its counterpart in 

 inorganic nature. If hydrogen and oxygen be brought to- 

 gether at ordinary temperatures there is "nothin' doin' ' 

 to use the English language up to date. But introduce a 

 little finely divided platinum into the situation, and under 

 its seemingly magic influence combination occurs and drops 

 of water form where before there was but gas. The heat 

 generated by this reaction soon raises the platinum to a red 

 heat and this principle was employed in the construction of 

 a self-lighting lamp, in which a jet of hydrogen played upon 

 a bit of spongy platinum, which soon heated igniting the 

 gas. The platinum here is known as a catalyzer. Its action 

 is similar to that of the ferment since it in some way brings 

 about a change in other substances, without itself entering 

 into that change. The activity of the ferment-forming cell 

 is responsible to itself for its continuation, for when the 

 products of ferment action become too great this action ceases, 

 and will not recommence until these products are removed, 

 or at least lessened in amount. 



Among vertebrate animals the digestive ferments are 

 formed chiefly by the stomach, pancreas and intestine, al- 

 though the liver, and in some instances the mouth glands 

 play a minor part ; while the simplified and soluble (digested) 



