Haughton's experiments, performed upon men, gave results which proved that no portion of the nitrogen of their food was lost by perspiration or by respiration. Barral, on the contrary, asserts that nitrogen is given off from the bodies of both man and the inferior animals. Boussingault states that horses, sheep, and pigs exhale nitrogen. A cow, giving milk, on which he had experimented, lost 15 per cent. of the nitrogen of its food by perspiration. The amount of nitrogen which Reiset states that sheep exhale is exceedingly great, and it is difficult to reconcile his results with those obtained by Voit, Bischoff, Regnault, Pettenkofer, and Haughton. Of course, men and sheep are widely different animals; but still it is unlikely that all the nitrogen of the food of man should be recoverable in his egesta, whilst nearly a third of the nitrogen of the food of the sheep should be dissipated as gas. I think further experiments are necessary before this point can be regarded as settled; and it is probable that it will yet be found that all, or nearly all, of the nitrogen of the food of animals is recoverable in their egesta. Regarding, then, an animal as a mechanism by which meat is to be "manufactured," five economic points in relation to it demand the feeder's attention: these are--the first cost of the mechanism, the expense of maintaining the mechanism in working order, the price of the raw materials intended for conversion into meat, the value of the meat, and the value of the manure. In proportion to the attention given to these points, will be the feeder's profits; but they are, to some extent, affected by the climatic, geographic, and other conditions under which the farm is placed. * * * * * [Footnote 1: If the elements were only capable of combining with each other in simple ratios, the number of their combinations would be as limited as that of the letters of the alphabet; but as one, two, or more atoms of oxygen can combine with one, two, or more atoms of other elements, we can assign no limits to the number of _possible_ combinations. There are hundreds of distinct substances formed of but two elements, namely, hydrogen and carbon.] [Footnote 2: In a paper by Professor Sullivan, of Dublin, the conversion of one of these substances into another _outside_ the animal mechanism, is almost incontrovertibly proved.] [Footnote 3: _Experimental Inquiry into the Composition of some of the Animals Fed and Slaughtered as Human Food._ By John Bennet Lawes, F.R.S., F.C.S., and Joseph Henry Gilbert, Ph.D., F.C.S. _Philosophical Transactions of the Royal Society._ Part II., 1860.] [Footnote 4: From the Greek _plasso_, "to form." Plastic materials are sometimes termed _formative_ elements; both terms imply the belief that they are capable of giving shape, or form, not only to themselves, but also to other kinds of matter not possessed of formative power.]