( 31 6 
DR. PROUT ON ANIMAL CHEMISTRY. 
nitric acid, in such a way that the two shall mix gradually; when, 
after a greater or less time, according to the proportion of urea 
present, the peculiar crystalline pearly compound, which I here 
shew you, is formed. Urine having an excess of urea is usually 
of considerable specific gravity (between 1020 and 1030), and is 
often accompanied by many symptoms somewhat like diabetes, 
for which the complaint has been occasionally mistaken ; but it 
differs from diabetes in being a curable disease, or at least, by 
care and attention, it can be so far subdued as to be rendered little 
* * 
troublesome. 
The next substance on which I shall make a few remarks is 
the cystic oxide . This is of very rare occurrence, and is mentioned 
here rather as a curiosity. Its properties you will find detailed in 
all chemical works. One of the most remarkable of these, and 
by which it can be readily distinguished, is the peculiar smell it 
yields when heated. This, as it cannot be described, I here ex¬ 
hibit to you. From the little that is known of this substance, it 
would appear to be generally connected with organic disease. 
The last substance on which I think it necessary to make a few 
remarks, is the lit hie acid , and some of its products. This prin¬ 
ciple, in many points of view, constitutes one of the most im¬ 
portant principles occurring in the urine. In the first place, it 
gives origin to stone in the bladder, in at least two instances 
out of three; secondly, combined with ammonia, it constitutes 
the basis of the most usual sediments occurring: in the urine: 
combined with soda, it gives origin to the gouty chalk-stone, and 
sometimes to sediments in the urine, and even concretions in the 
bladder. When modified it is converted into the purpuric acid, 
the principle constituting the colouring matter of the lateritious 
and pink sediments, and which are generally essentially com¬ 
posed of the lithate of ammonia, as before mentioned. 
The lithic acid, when pure, is a perfectly white crystalline 
powder, very insoluble in water, but readily soluble in alkalies, 
and forming various compounds with them. When first preci¬ 
pitated cold from its solution in potash, it exists in the state of a 
hydrate, and assumes the form of a bulky gelatinous mass, 
which does not begin to crystallize for a considerable time. This 
is a very important point connected with the pathological history 
of this principle, as the state above alluded to is that in which it 
is first separated from the kidneys, and often exists in the urine, 
and the knowledge of which will enable us to explain almost all 
the phenomena of lithic acid gravel. 
The lithate of ammonia is principally distinguished from lithic 
acid by its greater solubility in water, and by its yielding am- 
