It is obvious that the composition of the fæces will vary with the food given, and in this connexion it may be stated that the puer used was obtained from dogs fed on a mixture of boiled horseflesh and oatmeal porridge, about equal quantities. Sometimes charcoal and cabbage are mixed with the food, in this case the puer is very dark coloured. The dark colour so produced is to be carefully distinguished from the dark colour caused by decomposition of the puer.
We cannot leave out of account the urinary products, which, in the case of dung from hunting kennels, are always present, though in varying quantities.
The total nitrogen in 1520 c.c. of urine was found[23] to be 15·9 grm.
Each 100 grm. total nitrogen was distributed as follows:—
| Urea | 85 | ·9 |
| NH3 | 4 | ·1 |
| Creatinine | 3 | ·3 |
| Uric acid | 0 | ·5 |
| N in other compounds | 5 | ·7 |
The inorganic compounds were:—
Per cent. | ||
| Sulphur (as sulphate) | 3 | ·31 |
| P2O5 | 3 | ·98 |
| Cl | 6 | ·30 |
The urine of carnivora is acid, that of herbivora is neutral or alkaline.
Urea, which is the chief nitrogenous constituent, is very quickly fermented by several species of bacteria, and entirely decomposed into ammonium carbonate, so that it is this latter body which acts in the bate.