54 THE ZOOLOGIST. 



matter ; 2nd, a white or yellowish white substance, composed of 

 nearly pure uric acid, — so nearly pure that it is purchased for use 

 as a chemical reagent, — with a little urate of lime and ammonia, 

 oxalate of lime, purpurate of ammonia (the latter discovered by 

 Prout, and yielding a magnificent crimson colour known as 

 murexide), and a few other salts in veiy trifling quantities ; 3rd, 

 more or less water, containing some of these salts in solution. 

 During derangement these three become blended together some- 

 times. As would naturally be expected, there is more uric acid 

 and less simple excreinentitious matter in the dejecta of snakes 

 which live on frogs and fish than in those whose food consists of 

 birds and animals ; while it reaches its maximum in one which 

 has been persuaded to gorge itself on raw meat — as may 

 occasionally be effected with some Colubers : I have known the 

 Moccassin {Tropidonotus fasciatus) and Xenodon rhabdocepkalus 

 take dead meat in default of anything else. The freces of a 

 serpent probably yield more correct results when examined with 

 a view to determining the proportionate relation of their con- 

 stituents in character and quantity to that of the food taken than 

 those of any other creature, from its habit of feeding copiously 

 and at long intervals, and consequently the definite nature of its 

 meals; the progress of the food may also usually be traced 

 externally in its passage from the mouth to the anus, so that we 

 have no hesitation in saying what it is — frog, bird, or beast, of 

 such and such a weight — that is furnishing us with details. It is 

 for this reason that one is able to exclude uric acid in investigation 

 of the active principle of the excretory cutaneous exudation, 

 since the whole possible amount can be accounted for in the 

 faecal evacuation. Now, it is found that external heat quickens a 

 reptile's digestion — to use a common phrase which is not quite 

 correct in its strict application, since by it is meant only that it 

 hastens the process of defecation after a meal. Warmth, on 

 which a snake's activity so much depends, doubtless increases the 

 peristaltic action of its intestine in common with the rest of the 

 muscular system ; and if the fasces be analysed they will be found 

 to contain less evidence of utilised nitrogenous elements in the 

 form of uric acid, and more unused digestible matter. Thus 

 the snake really derives less benefit from " quick digestion" than 

 from slow, because the former is incomplete and allows it to 

 extract less nutriment. The question which has suggested itself 



