Proteids.
| | Albumen. | Caseine. | Syntonin. | Gluten. | Gelatine. |
| Carbon, | | 72 | | | |
| Hydrogen, | | 112 | | | |
| Oxygen, | | 23 | | | |
| Nitrogen, | | 18 | | | |
| Sulphur, | | 1 | | | |
| Phosphorus, | | R. 2 | | | |
Non-Nitrogenous Substances.
| | Carbon. | Hydrogen. | Oxygen. |
| 1. | Starch (amyloids), | 18 | 30 | 15 |
| | Sugar cane, | 12 | 22 | 11 |
| 2. | Oils and fats composed of stearic acid of mutton or beef, | 18 | 36 | 2 |
| 3. | Mineral—Saline matters, as chloride of sodium, phosphate of lime. | | | |
Animals cannot subsist on any but organic substances, and these must contain the elements which are naturally combined with them—in other words, not even organic compounds are nutritive unless they are supplied in their natural state. Pure fibrine, pure gelatine, and other principles purified from the substances naturally mingled with them, are incapable of supporting life for more than a brief time. Moreover, health cannot be maintained by any number of substances derived exclusively from one only of the two chief groups of elementary principles mentioned above. A mixture of nitrogenous and non-nitrogenous organic substances, together with the inorganic principles which are severally contained in them, is essential to the well-being, and generally even to the existence, of an animal. The truth of this is demonstrated by experiments performed for the purpose; and is also well illustrated by the composition of the food prepared by nature as the exclusive source of nourishment to the young mammals, namely milk. The composition of milk is:
| | Human. | Cow’s. |
| Water, | 890 | 858 |
| Solids, | 110 | 142
|
| | 1000 | 1000
|
| Caseine, | 35 | 68 |
| Butter, | 25 | 38 |
| Sugar (with extracts), | 48 | 30 |
| Salts, | 2 | 6
|
| | 110 | 142 |
| | Carb. | Hyd. | Nit. | Oxy. | Sulph. | R (unknown). |
| Caseine, | 72 | 112 | 18 | 23 | 1 | 2 |
In milk, it will be seen from the preceding table, the albuminous group of aliments is represented by the caseine, the oleaginous by the butter, the aqueous by the water, the saccharine by the sugar of milk.
Let us compare the composition of these four organic substances and water:
| | Oxy. | Hyd. | Carb. | Nitr. | Sulph. | R (unknown element). |
| Water, | 1 | 2 | | | | |
| Sugar, OH2+ | 11 | 22 | 12 | | | |
| Caseine, | 23 | 112 | 72 | 18 | 1 | 2 |
| Olein, | 6 | 38 | 21 | | | |