698 SCIENCE PROGRESS 



which not only differ in construction but which — when taken 

 to pieces — turn out to be made of bricks of very different sizes 

 and shapes, perhaps twenty or more ; and not only so, for the 

 different buildings are found to contain the different-sized bricks 

 in different proportions. This point is a very important one. 

 To give an illustration. Wheat gluten on digestion yields about 

 a third of its weight of a particular amino-acid — glutaminic 

 acid — which is quite a minor constituent of most animal 

 albuminoids. What becomes of this particular kind of brick — 

 of this particular product of animal digestion — when flour is 

 consumed by us ? It is certain that it is only in part assimilated ; 

 but before the unassimilated portion can escape from the body, it 

 must be completely burnt up. The value of flour as food must 

 depend on whether it is burnt up to a considerable extent 

 usefully or merely in order that it may be got rid of. If the latter 

 be the case, work is thrown unnecessarily upon the organs which 

 effect the change. In any case, much of the nitrogen is wasted, 

 being useless as fuel. Per contra, certain constituents of our 

 food, present in very minute quantity, are nevertheless probably 

 of utmost consequence as furnishing the necessary means of 

 constructing some particular all-essential part of the animal 

 mechanism. To supply the required amount of such material, 

 it may be necessary to consume considerable quantities of the 

 ordinary foods ; the use of a more concentrated form of the material 

 would presumably be of great advantage. Until questions such 

 as these are solved, stock-raising and the maintenance of health 

 must be subject to purely empirical rules. Some of you will 

 know that there has been considerable discussion of late on the 

 nutritive value of various kinds of bread and on the selection of 

 seed calculated to give a good wheat. Probably the discussion 

 is entirely premature — we simply don't, know what constitutes 

 a good wheat ; there is no accepted standard of goodness. 

 What is called strength is a purely fictitious expression with 

 regard to the food-value of flour ; it has reference merely to 

 the power of the flour to carry water and to its stickiness— the 

 " strongest " flour being one from which the baker can make 

 the greatest number of loaves and the biggest loaf; it is there- 

 fore the weakest as a food material. 



While the office of nitrogenous manures as contributing 

 a necessary material to the formation of albuminoids and that of 

 phosphates as contributing to the formation of nuclear elements 



