400 NUTRITION. 



greater or lesser necessity for one or more of these elements, for 

 the maintenance of its integrity, as well as for the production of 

 certain effects of force. These questions must be solved by quan- 

 titative determinations, for the physiologico-chemical statistics of 

 the living organism are not alone competent to elucidate this sub- 

 ject. We need scarcely observe, that in judging of the nutritive 

 value of an article of food, we must not lose sight of the quality of 

 the nutritive elements belonging to the different groups, since this 

 in a great measure determines its digestibility. Hard-boiled white 

 of egg, meat that has been boiled for a long time, and hard cheese 

 which is poor in fat and in salts, are less easily digested than soft- 

 boiled or fresh white of egg, meat steeped in vinegar, or slightly 

 coagulated moist and rich cheese; starch is much more rapidly 

 converted into sugar when boiled than in its raw form, when, as we 

 have already seen, it frequently and principally passes off in an 

 un: hanged state, whilst another carbo-hydrate, namely cellulose, is 

 only employed as food by certain animals under special relations. 

 Notwithstanding their identity of constitution, the members of the 

 same group frequently exhibit very great differences, depending 

 upon their greater or lesser accessibility to the agents of digestion. 

 An article of food may, therefore, owing to the indigestibility of its 

 constituents, frequently possess a far less nutritive value than we 

 should expect from the mixture and composition of its elements 

 of nutrition. It must not, therefore, be wholly forgotten, that 

 the digestibility of a substance constitutes one of the factors of its 

 nutritive value. As, however, this subject closely corresponds with 

 all that has already been stated in reference to the digestibility of 

 the different nutrient matters, we will now revert to the main ques- 

 tions already noticed, the former of which considered the proper 

 admixture of the individual elements of nutrition in the nutrient 

 substance. Before we proceed to decide the question of what are 

 the most favourable proportions of these four fundamental nutrient 

 matters in any one article of food, (and, therefore, how the normal 

 nutrient matter must be constituted in order, under the common 

 relations, to yield to the animal organism the materials neces- 

 sary for the fulfilment of all its functions, as well as for the 

 renovation of effete matters,) it will not be out of place to consider 

 from this point of view the composition of the ordinary articles 

 of food. 



As the nitrogenous constituents of the nutrient matters, that is 

 to say, the albuminates, are principally employed in the reproduc- 

 tion of the tissues, and of the actual organs of the animal organism, 



