584 GENERAL METABOLISM [CH. XXXIX. 



Supposing the body to remain in the condition produced by these 

 anabolic processes, what is its composition ? A glance through the 

 chapters on the cell, the blood, the tissues, and the organs will con- 

 vince the inquirer that different parts of the body have very different 

 compositions ; still, speaking of the body as a whole, Yolkmann and 

 Bischoff state that it contains 64 per cent, of water, 16 of proteids 

 (including gelatin), 14 of fat, 5 of salt, and 1 of carbohydrates. The 

 carbohydrates are thus the smallest constituent of the body; they 

 are the glycogen of the liver and muscles, and small quantities of 

 dextrose in various parts. 



The most important, because the most abundant of the tissues of 

 the body, is the muscular tissue. Muscle forms about 42 per cent, 

 of the body-weight,* and contains, in round numbers, 75 per cent, of 

 water and 21 per cent, of proteids; thus about half the proteid 

 material and of the water of the body exist in its muscles. 



The body, however, does not remain in this stable condition ; even 

 while nutrition is occurring, destructive changes are taking place 

 simultaneously; each cell may be considered to be in a state of 

 unstable equilibrium, undergoing anabolic, or constructive processes, 

 on the one hand, and destructive, or katdbolic, processes on the other. 

 The katabolic series of phenomena commences with combustion ; the 

 union of oxygen with carbon to form carbonic acid, with hydrogen 

 to form water, with nitrogen, carbon, and hydrogen to form urea, 

 uric acid, creatinine, and other less important substances of the same 

 nature. The formation of these last-mentioned substances, the 

 nitrogenous metabolites, is, however, as previously pointed out, partly 

 synthetical. The discharge of these products of destructive metabol- 

 ism by the expired air, the urine, the sweat, and faeces is what con- 

 stitutes excretion ; excretion is the final act in the metabolic round, 

 and the composition of the various excretions has already been con- 

 sidered. 



An examination of the intake (food and oxygen) and of the out- 

 put (excretion) of the body can be readily made ; much more readily, 

 it need hardly be said, than an examination of the intermediate steps 

 in the process. A contrast between the two can be made by means 

 of a balance-sheet. A familiar comparison may be drawn between 

 the affairs of the animal body and those of a commercial company. 

 At the end of the year the company presents a report in which its 

 income and its expenditure are contrasted on two sides of a balance- 

 sheet. This sheet is a summary of the monetary affairs of the under- 

 taking ; it gives few details, it gives none of the intermediate steps 

 of the manner in which the property has been employed. This is 



* The following is in round numbers the percentage proportion of the different 

 structural elements of the body: skeleton, 16; muscles, 42; fat, 18; viscera, 9; 

 skin, 8 ; brain, 2 ; blood, 5, 



