DIETETICS 149 



suggest any prejudice with regard to its chemical constitution. 

 Within the meshes of the bioplasm are nutrient materials, 

 as yet unused, and worked-up products in various stages. It 

 has always been taken for granted that when treating of nutri- 

 tion, we have to consider the repair of the bioplasm, as well as 

 the provision of raw material which it can convert into the 

 specific products of the cell. Suppose that the cell belongs 

 to the class of supporting tissues ; let it be a cell of cartilage, 

 for example. The bioplasm manufactures a collagenous sub- 

 stance which remains in and around its meshwork. If it be 

 an epidermal cell, it forms horny substance. If a secreting 

 cell, it accumulates secernable products. If a muscle-cell, it 

 develops a large quantity of material, which by a change in 

 form produces movement. In this last case we suppose that 

 the energy set free as muscular force is due to oxidation. 

 More stable bodies take the place of a less stable substance. 

 After contraction the relatively complex contractile material 

 is renewed from the foods stored in the muscle-cell ; or if it 

 be not, in the ordinary sense of the word, destroyed, if it has 

 merely parted with certain oxidizable constituents, it obtains a 

 fresh supply of such constituents from the foods which the 

 muscle-cell contains. Even in the case of cartilage or epidermis, 

 we imagine that, since the matrix is " alive," it is always under- 

 going molecular change, and consequently always requiring 

 food. The fact that every tissue, however inert, dies when, 

 owing to the blocking of the bloodvessels which irrigate the part, 

 its supply of nutriment is cut off, justifies this belief that all 

 living tissue is undergoing change. 



When we make up a balance-sheet of the body as a whole, 

 placing to the debit side the food which it receives, and to its 

 credit side the work done in external movement and in 

 the production of heat, we again find reason for believing 

 that every part of every cell is constantly undergoing 

 change. 



The balance-sheet of the body can be drawn out in either 

 of two ways. We can estimate the quantities of nitrogen, 

 carbon, hydrogen, and oxygen supplied to it in the several 

 foods, and compare them with the amounts of each of these 

 four elements given off in urea, carbonic acid, and water, 

 making, of course, a note of the body's balance in hand at 



