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10. J. That secretion is not a mechanical process is proved 

 by these facts: 1st, that the structure of the secreting organs re- 

 mains after death; and if a.part of the blood were separable by this 

 structure in the way of filtration, the injection of blood into the 

 supplying arteries of the organ should be followed by the separa- 

 tion of that peculiar fluid, which is precisely fitted to transude 

 through such a peculiar structure. Against the force of this argu- 

 ment it might be objected, filtration, or mechanical secretion, sup- 

 poses a precise adaptation of certain particles to tubes of a certain 

 area or figure, and these being left after death with no other 

 power to regulate their area except that of elasticity, a force cor- 

 rectly imitating the natural one of the circulation may impel into 

 these tubuli particles of a different order, thus substituting another 

 for the secretion of the living state. According to this objection, 

 a dependence of secretion upon properties of life is acknowledged ; 

 but the dependence is thus supposed to be upon a vital contrac- 

 tility, which has no other effect than to regulate the capacity of 

 tubuli. But the objection itself (founded indeed only upon a 

 possible fact) assumes that the component particles of different 

 fluids are of different shapes and sizes; some fluids no doubt are 

 capable of a more minute divisibility by the operation of the same 

 agents than others. We find that clear thin fluids will transude 

 readily through substances into which the thick or viscid ones will 

 not pass. Hence the variety of the divisibility of fluids seems to 

 be that rnore numerous particles of some cohere and make up 

 larger molecules, while fewer particles of others cohere and make 

 up lesser molecules; hence the separable masses of some are large, 

 and those of others small; the former fitted to permeate only large 

 interstices or tubuli of large area, and the latter capable of per- 

 meating those of a smaller size. It is hence obvious that the tubes 

 which are large enough to admit (or secrete) fluids composed of 

 the largest molecules, must at least admit at the same time, those 

 composed of the smallest ones, both existing in one common source. 

 Hence urine or sweat should run abundantly through the tubuli 

 testis, which admit the most viscid secretion; and all the mucous 

 and synovial membranes should pour out milk, bile, urine, lymph, 

 \vater, or blood itself, rather than, or at least mixed with, those 

 thick, infiltrable juices which they are found to produce. Such, 

 however, is not the fact; and secretion in this view, as it does also 

 in many others, appears to be governed by laws very different 

 from those of the mechanical process just considered. 



11. That secretions are not produced, or elected, or sepa- 

 rated from the blood by chymical affinity appears satisfactorily 

 proved by the facts before insisted upon, viz. that these secretions 

 do not continue after death, &c. If it should be urged, in objec- 

 tion to this proof, that we do not know but the chyrnical proper- 

 ties may undergo a change at the time of death, I ask what are 

 those properties I The chymical properties of substances remain 

 as long as the substances to which they belong, aud whkh they 



