THE OPPORTUNITY OF THE AGRICULTURIST 697 



carbohydrates ; the process is certainly a directed process and 

 doubtless they also are constructed on an enzymic model or last. 

 Hitherto, little attention has been paid to the production of 

 quality, in the chemical sense, either in plants or animals ; 

 quantity and certain characteristics have mainly been in demand. 

 Now we are beginning to realise that quality must be attended 

 to— that we know little or nothing at present, except empirically, 

 of our own requirements and still less of those of agricultural 

 stock. Man has just felt his way by picking and choosing and 

 reason has played but a small part in determining his choice of 

 food. The time is at hand when in feeding ourselves and our 

 stock we must be guided more by scientific principles. 



Food is of value to animals from two points of view— as the 

 source of energy and as constructive material. It is only of 

 value in so far as it is digestible — that is to say, in so far as 

 the enzymes are at our disposal which are capable of taking its 

 complex constituents to pieces and rendering them soluble and 

 transmissible to various parts of the body. The carbohydrates 

 are of value mainly as fuel ; they are required in relatively small 

 quantity as constructive materials. 



The function of the albuminoids or proteins as constructive 

 materials is clear — that they serve also as fuel cannot be doubted ; 

 but we have little idea at present to what extent they are 

 necessary, if at all, as the source of energy. The animal 

 mechanism is of extraordinary complexity — its parts differ much 

 in composition, being constructed of very different nitrogenous 

 materials ; and there are also great differences between the 

 nitrogenous materials of different origin, whether animal or 

 vegetable. 



We may compare the digestion of food with the pulling 

 down of a building by housebreakers. Not long ago it was 

 supposed that digestion— at least, in its earlier stages — involved 

 the breaking down of the complex albuminoid structures into a 

 few simpler but, at the same time, still complex sub-groups ; 

 and that these were then assimilated and re-united to form the 

 animal tissue. This view has given place of late to the idea 

 that the simplification of the albuminoids is carried very far — 

 in fact, down to the ultimate units, such as leucine, tyrosine, 

 etc. ; it is supposed that the tissues are reconstructed from 

 these very simple materials. 



The albuminoids generally may be contrasted with buildings 



