[Footnote 5: The slow conversion of phosphorus into phosphoric acid takes place in the animal organism; its gradual oxidation in the open air gives rise only to an imperfectly oxidised body--_phosphorous acid_. But the latter fact does not invalidate the general proposition, that the heat emitted by a substance undergoing the process of oxidation is proportionate to the amount of oxygen with which it combines, and is not influenced by the length of time occupied by the process, further than this, that if the oxidation be _very_ rapidly effected, a portion of the heat will be converted into an _equivalent_ amount of light.] [Footnote 6: This statement is not absolutely correct, but the range of variation is confined within such narrow limits as to be quite insignificant.] [Footnote 7: Doubt has recently been thrown on the truth of this belief by Frankland, Fick, and Wislicenus.] [Footnote 8: The results of Savory's experiments on rats appear to prove that animals can live on food destitute of fat, sugar, starch, or any other fat-forming substance. I think, however, that animals could hardly thrive on purely nitrogenous food. The conclusions which certain late writers, who object to Liebig's theory of animal heat, have deduced from Savory's investigations, appear to me to be quite unfounded.] [Footnote 9: So termed because it is the basis of the common oils; the fluid portion of fat is composed of oleine.] [Footnote 10: The term _dry_ is applied to the _solid_ constituents of the food. Thus, a pig fed with 100 lbs. of potatoes would be said to have been supplied with 25 lbs. of dry potatoes, because water forms 75 per cent. of the weight of those tubers.] [Footnote 11: The amounts of "mineral matter" are too high, owing to the adventitious matters (dirt) retained by the wool.] [Footnote 12: This pig was completely analysed by Lawes and Gilbert.] [Footnote 13: The results of recent and accurately conducted investigations prove that men engaged in occupations requiring the highest exercise of the intellectual faculties, require more nutritious food, and even a greater quantity of nutriment, than the hardest worked laborers, such as paviours, and navvies. I have been assured by an extensive manufacturer, that on promoting his workmen to situations of _greater_ responsibility but _less_ physically laborious than those previously filled by them, he found that they required more food and that, too, of a better quality. This change in their appetite was not the result of increased wages, which in most cases remained the same--the decrease in the amount of labour exacted being considered in most cases a sufficient equivalent for the increased responsibility thrown upon them.] [Footnote 14: As ammonia, urea, uric acid, or hippuric acid; all of which are nearly or perfectly mineralised substances.] [Footnote 15: The excrements of animals are capable of evolving, by combustion, enormous amounts of heat.] PART II.