PHYSIOLOGY, 
speedily irritated by their presence ; and is 
performed partly by the muscular coat of 
that intestine, and partly by the muscles of 
respiration, producing the effort called 
straining. The periods of voiding the ex- 
crement vary, from several causes : they 
are more frequent in the young subjects, 
where the stools are more liquid. In the 
adult they should not be less, in a healthy 
state, than puce in twenty-four hours. 
Urinary Secretion. The liquids which we 
drink, absorbed by the lacteals, together 
with the nutritive part of the solid aliment, 
dilute the latter, and serve as a vehicle for 
it. They increase tlie quantity of the blood, 
and render it more fluid ; conveyed into 
every part of the circidating system, they 
penetrate all our organs, carry away the 
particles detached from them in the dif- 
ferent vital processes, and are then sepa- 
rated from the mass of fluids by the urinary 
organs, together with various other sub- 
stances, whose retention in the body would 
produce injurious effects. The kidneys, 
therefore, dispose of the residual part of our 
liquid ingestu, as the feces are formed by 
the more solid foods, and the quantity of 
urine may, of course, be expected to vary 
according to that of the drink. All the old 
parts of the frame, which are constantly re- 
moved by the absorbents, while new depo- 
sitions are formed by the nutrient arteries, 
go off in the same way; and hence the 
urine, although apparently a watery fluid, 
and called in common language water, con- 
tains a great deal of animal matter. 
From the above account it will be readily 
understood, that the properties of the urine 
must vary according to the time at which it 
is voided after meals ; the quantity of food 
and drink, the age and complaints ofujdi- 
viduals, &c. Physiologists have distinguish- 
ed urine of the drink, chyle, and blood. 
The first is a watery fluid, almost colourless, 
evacuated very soon after drinking, and 
possessing very slight urinous characters; 
the second, evacuated two or three hours 
after meals, is better elaborated, but not 
yet complete in its constituent principles ; 
the last, voided after the repose of the 
night, has all the properties of urine in an 
eminent degree. In infants it possesses no 
phosphate of lime nor phosphoric acid, as 
those substances are employed in the busi- 
ness of ossification, which is then active. 
In old persons, on the contrary, where the 
bony system, already overcharged with 
phosphate of lime, refuses to admit any 
more, this substance is carried off by the 
kidneys. It is removed in the same way in 
rachitis and mollities ossium, where the 
bones become softened by its absence. 
The great quantity of saline and crystal- 
lizable elements contained in the urine, ac- 
count for the frequency of calculous con- 
cretions, which are found by recent and 
accurate analysis to vary very considerably 
in their composition. As there is no sub- 
stance in the body which may not be' eva- 
cuated by the urine, and manifest itself in 
that liquid, so, under different circum- 
stances, every thing possessing a power of 
concretion may become the subject- of 
urinary calculus. This diversity of consti- 
tuent elements, together with the want of 
cjiaracteristic symptoms of the different 
species ; and the irritation which the coats 
of the bladder must experience from che- 
mical reagents, will convince us how ex- 
tremely difiicult, if not impossible, it must 
be to discover a lithontriptic that would 
obviate the necessity of a surgical opera- 
tion. 
The urine is very speedily and sensibly 
affected by certain substances ; thus aspara- 
gus occasions a remarkable foetor in this 
fluid : and turpentine imparts to it a violet 
odour. For a further account of its com- 
position and physiology see the article 
Urine. 
Almost every physiologist has noticed the 
rapidity with which this secretion is carried 
on : aqueous fluids, taken by the mouth, 
are sometimes separated so quickly by tlie 
kidneys, that an immediate communication 
has been suspected between the stomach 
and kidneys, on the supposition that there 
had not been a sufficient time tor the fluid 
to arrive at the latter organ in the regular 
course of absorption and circulation. This 
conjecture derives no countenance from 
anatomy, and the size of the renal vessels 
explains the fact without any such suppo- 
sition. 
Absorption, or the process by which the 
chyle, separated from the food by the 
digestive organs, is carried into the blood, 
naturally follows the account of digestion. 
We have very little to add to what is 
stated on this subject in the article Ana- 
tomy, 
The admission of matter into the orifices 
of the absorbing vessels has been accounted 
for in various ways. Some physiologists 
consider it as a case of capillary attraction. 
But a little reflection is sufficient to shew 
that tlie absorbents are not like capillary 
tubes immersed in a fluid. Besides, were 
