520 APPENDIX. 



dissolve when boiled with a solution of potash. It contains 

 nitrogen and sulphur, though in small proportions. The products 

 of its decomposition have not yet been investigated. Marcet 

 considers that it exists for the most part in a free state in the 

 excrements, and constitutes one of their immediate principles. 

 As to its source, he observes that it appeared in excess when a 

 considerable quantity of beef had been taken, and in less than the 

 usual quantity in a case of diarrhoea attended with loss of appetite ; 

 but none could be directly obtained from beef on subjecting it to 

 the same process of extraction as faeces ; neither could it be found 

 in ox-bile, the urine, or the substance of the spleen. 



2. A fatty acid having the properties of margaric acid, but not 

 constantly present. He is uncertain whether the margaric acid 

 in the feeces is free, or combined with excretine, but he is disposed 

 to conclude that the neutral fats are decomposed in the intestinal 

 canal, and their acid set free. Not having been able to discover 

 stearic acid in human evacuations, he supposes that what is con- 

 tained in the fat taken in the food must be converted into margaric 

 acid in its passage through the alimentary canal. 



3. A colouring matter similar to that of blood and urine. 



4. A light granular substance, which he is inclined to regard 

 as a combination of phosphate of potash and a pure organic 

 matter. 



5. An acid olive-coloured substance, of a fatty nature, which 

 he names excretolic acid. It fuses between 25 and 26 C., and at 

 a higher temperature burns without residue. It is insoluble in 

 water and in a boiling solution of potash, is very soluble in ether, 

 and in hot alcohol, and slightly so in cold water. He believes 

 that it is combined in the excrements in the form of a salt with 

 excretine or a basic substance closely allied to it. 



6. No evidence of butyric or of lactic acid was obtained. 

 The feeces of various animals yielded the following results : 



1. The excrements of carnivorous mammals, viz., the tiger, 

 leopard, and dog (fed on meat) contain a substance allied in its 

 nature to excretine, but not identical with it. They contain no 

 excretine, but yield butyric acid, which is not present in human 

 excrements. 



2. The excrements of the crocodile contain cholesterin, and no 

 uric acid, while those of the boa yield uric acid, and no cholesterin. 

 [It is probable that the semi-solid urine and the excrements were 

 not duly separated in this experiment. G. E. D.] 



3. The faeces of herbivorous animals, viz., the horse, sheep, 



