582 GENERAL METABOLISM. [CH. xxxix. 



state of unstable equilibrium, undergoing anabolic, or constructive 

 processes, on the one hand, and destructive, or katabolic, 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, how- 

 ever, as previously pointed out, partly synthetical. The discharge 

 of these products of destructive metabolism by the expired air, 

 the urine, the sweat, and faeces is what constitutes excretion ; excre- 

 tion is the final act in the metabolic round, and the composition 

 of the various excretions has already been considered. 



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

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

 readily, it need hardly be said, than an examination of the inter- 

 mediate 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 6"f 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 undertaking ; it gives few 

 details, it gives none of the intermediate steps of the manner in 

 which the property has been employed. This is given in the 

 preliminary parts of the report, or may be entered into by still 

 further examining the books of the company. 



In the parts of this book that precede this chapter I have 

 endeavoured to give an account of various transactions that 

 occur in the body. I now propose to present a balance-sheet. 

 Those who wish still further to investigate the affairs of the 

 body may do so by the careful study of works on physiology ; 

 still, text-books and monographs, however good, will teach one 

 only a small amount ; the rest is to be learnt by practical 

 study and research ; and we may compare physiologists to the 

 accountants of a commercial enterprise, who examine into the 

 details of its working. Sometimes, in business undertakings, a 

 deficit or some other error is discovered, and it may be that the 

 source of the mistake is only found after careful search. Under 

 these conditions, the accountants should be compared to 

 physicians, who discover that something is wrong in the working 

 of the animal body ; and their object should be to discover where, 

 in the metabolic cycle, the mistake has occurred, and subsequently 

 endeavour to- rectify it. 



