THE NORMAL QUANTITY OF FOOD. 407 



animal functions, mental excitement, &c, necessarily call for a 

 restoration of the material parts lost in the different processes. 

 This is so clear that there can scarcely be a doubt on the subject ; 

 but we are still entirely in the dark in reference to the more exact 

 determinations of the proportions which are required to enable us 

 to calculate the composition of the food, which is best adapted for 

 each special organism. The physiologist should, however, attempt 

 to calculate for a given organism under certain definite conditions, 

 the proportion in which the special nutrient matters ought to be 

 mixed in order that the persistent well-being of the organism may 

 be secured ; and in this respect physiology has the best prospect of 

 attaining to determinate numerical values ; from these we may 

 then construct general formulae, by means of which we may be 

 enabled to predict with mathematical certainty the result of any defi- 

 nite action upon the animal organism. The functions which must be 

 considered in a formula of this kind are certainly very numerous, and 

 very many investigations have still to be made before this object 

 can be attained. But if this be an extensive field whose cultivation 

 is still beset with great difficulties, it yet promises the richest 

 results which may not only influence theory, but which will also 

 make a marked impression upon practical life. Dietetics would 

 then be based upon a firmer foundation, and it will no longer remain 

 a mere illusive idea that the healing art may be made accessible to 

 exact inquiry. 



A more important question than the determination of the rela- 

 tions of mixture in different articles of nutrition is that of the absolute 

 quantities of food which are requisite for the maintenance of life, 

 and for the energetic accomplishment of all its functions. A very 

 great number of observations which contribute towards the solution 

 of this question have been made on man as well as on animals. 

 These investigations have, however, been conducted rather with 

 the view of comparing together the excreta of the animal organism 

 generally, and of finding some standard for the amount of the 

 metamorphosis of animal matter, than with special reference to the 

 question of the quantities of favourably mixed food, which the 

 organism requires for its natural well-being. If for the present we 

 put these investigations entirely out of the question, and consider 

 the methods by which we may determine the amount of food 

 which is necessary to the organism, we find that there are two 

 modes of determination which especially present themselves to our 

 notice. The first method consists in experimenting upon oneself 

 or upon animals with the smallest possible quantities of differently 



