PHYSIOLOGY. 



tible parts of* vegetables, as the skin of 

 fruits, husks of grain, &c. The latter, 

 indeed, is so little affected by the powers 

 of digestion, that when the covering is 

 entire, a grain may pass through the 

 body, and still retain the power to ger- 

 minate. 



The expulsion of the feces take place 

 when they arrive in the rectum, which is 

 speedily irritated by their presence ; and 

 is performed partly by the muscular coat 

 of that intestine, and partly by the mus- 

 cles of respiration, producing the effort 

 called straining. The periods of voiding 

 the excrement vary, from several causes : 

 they are more frequent in the young sub- 

 jects, where the stools are more liquid. 

 In the adult they should not be less, in a 

 healthy state, than once in twenty-four 

 hours. 



Urinary Secretion. The liquids which 

 we drink, absorbed by the lacteals, toge- 

 ther with the nutritive part of the solid 

 aliment, dilute the latter, and serve as a 

 vehicle for it. They increase the quan- 

 tity of tlie blood, and render it more 

 fluid ; conveyed into every part of the 

 circulating system, they penetrate all our 

 organs, carry away the particles detached 

 from them in the different vital processes, 

 and are then separated from the mass of 

 fluids by the urinary organs, together 

 with various other substances, whose re- 

 tention in the body would produce inju- 

 rious 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 con- 

 stantly removed by the absorbents, while 

 new depositions are formed by the nu- 

 trient arteries, go off in the same way ; 

 and hence the urine, although apparent- 

 ly a watery fluid, and called in common 

 language water, contains a great deal of 

 animal matter. 



Prom the above account it will be rea- 

 dily understood, that the properties of the 

 urine must vary according to the time at 

 which it is voided after meals, the quan- 

 tity of food and drink, the age and com- 

 plaints of individuals, &c. Physiologists 

 have distinguished urine of the drink, 

 chyle, and blood. The first is a wateiy 

 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 phos- 

 phate of lime nor phosphoric acid, as 

 those substances are employed in the bu- 

 siness 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 mollitiesossium, where 

 the bones become softened by its ab- 

 sence. 



The great quantity of saline and crys- 

 tallizable elements contained in the urine, 

 account for the frequency of calculous 

 concretions, which are found by recent 

 and accurate analysis to vary very consi- 

 derably in their composition. As there 

 it no substance in the body which may 

 not be evacuated by the urine, and mani- 

 fest itself in that liquid, so, undaf diffe- 

 rent circumstances, every thing possess- 

 ing a power of concretion may become 

 the subject of urinary calculus. This di- 

 versity of constituent elements, together 

 with the want of characteric symptoms of 

 the different species, and the irritation 

 which the coats of the bladder must es , 

 perience from chemical reagents, will ' 

 convince us how extremely difficult, if 

 not impossible, it must be, to discover a 

 lithontriptic that would obviate the ne- 

 cessity of a surgical operation. 



The urine is very speedily and sensi- 

 bly affected by certain substances ; thus 

 asparagus occasions a remarkable fee tor 

 in this fluid : and turpentine imparts to it 

 a violet odour. For a further account of 

 its composition 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 quick- 

 ly by the kidneys, that an immediate 

 communication has been suspected be- 

 tween the stomach and kidneys, on the 

 supposition that there had not been a suffi- 

 cient time for the fluid to arrive at the 

 latter organ in the regular course of ab- 

 sorption and circulation. This conjecture 

 derives no countenance from anatomy, 

 and the size of the renal vessels ex- 

 plains 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 foUows the account of diges- 

 tion. We have very little to add to what 



