268 
DR. JVIARCET ON THE IMMEDIATE PRINCIPLES OF 
ensues, nitrous acid fumes are evolved, and by concentrating the fluid on the water- 
bath, another substance is obtained, under the form of beautiful colourless crystals 
shooting from one side of the capsule to the other, and presently filling up the whole 
space the fluid occupied. This substance has a strong acid reaction, and is very 
soluble in water ; it attracts rapidly moisture from the atmosphere and deliquesces. 
However, although it may be interesting in a chemical point of view, as it is not a 
constituent of excrements, I shall not dwell any longer for the present upon its pro- 
perties. 
It was a matter of considerable importance to ascertain in what form excretine 
exists as a constituent of human faeces, and if this substance is one of their imme- 
diate principles. I have scarcely any doubt as to the greater proportion of excretine 
existing in the free state as a constituent of excrements, and therefore constituting, 
in that form, one of their immediate principles, as in several cases I have observed 
excretine crystallize directly in the alcoholic extract of faeces before the addition of 
lime. Moreover, although the lime precipitate generally yields, besides this sub- 
stance, an organic acid which I have found to be margarie acid, it is hardly possible 
to suppose that lime could have the property of so rapidly decomposing a combina- 
tion of margarie acid with excretine, should such a compound really exist. I have 
also ascertained by direct experiment, that if lime be added to a solution of margarie 
acid and excretine in alcohol, both are precipitated, the margarie acid combining 
with the lime, and the excretine adhering mechanically to the precipitate formed. 
It may consequently be assumed that the greater proportion, if not the whole of the 
excretine contained in human fceces, exists in the uncombined state, or as one of 
their immediate principles. 
Nothing positive is yet known in regard to the mode of formation of excretine in 
the human body. It may, however, be surmised that it is dependent in some degree 
on the nature of the alimentation ; at least I have noticed an excess of excretine 
when a considerable amount of beef had been taken, and, on the other hand, a 
smaller amount than usual of that substance was obtained in a case of diarrhoea 
attended with loss of appetite. Age and temperament do not appear to modify the 
production of excretine. 
In order to determine the source or mode of formation of excretine in the human 
body, and complete its physiological history, it will be necessary to ascertain — 
1st. Whether it exists in animal food or muscular tissue. 
2nd. In what part of the intestines it is first to be detected. 
3rd. Whether it can be found in any other part of the human body. 
4th. Whether it exists in the castings of animals. 
1st. With the view of ascertaining whether animal food or muscular tissue con- 
tained excretine, a sample of fresh beef, free from fat, was carefully minced, and 
treated with boiling alcohol ; a colourless extract was obtained, which being filtered 
through calico, and allowed to stand for some hours, yielded but a very scanty 
