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seated, and its division not to be accomplished without much ex- 

 traneous injury, some suspicions may arise on the truth of the 

 analogy upon which the inference is founded. 



18. We profess not to decide on matters which are necessarily 

 doubtful; on such we state alternatives, which in the present case 

 are, 1st, that secretions in general are produced by spiritual pro- 

 perties which live by assimilation in the organs of secretion; or, 

 2nd, that the secreting function of organs is aided by properties 

 derived from another seat; or, 3rd, that particular examples of 

 both these modes occur among these structures which perform 

 offices of secretion. 



19. Notwithstanding a mechanical secretion or filtration of 

 fluids through tubuli or pores has been rejected, it is necessary 

 that an adaptation should subsist in this respect. There are also 

 instances in which secretion appears to be superseded by a mere 

 hydraulic process, as when blood itself is forced through exhalents, 

 as in the serous membranes, &c. which effect results from, or at 

 least succeeds an increased impetus of the circulation. We find 

 this effect to take place in pneumonia, in nephritis, &c. and effu- 

 sion of blood by transudation is an occurrence which is said to take 

 place not unfrequently in the brain. 



20. Seeing then that this hydraulic process occurs some- 

 times, we are led to a wider consideration of the laws by which 

 in general specific secretions are formed and filtrations prevented. 

 Here we must recur in part to a statement of circumstances 

 already alleged. 



21. The tubuli of secerning structures, which admit without 

 impediment the most viscid fluids, should, according to their 

 mechanical construction, admit still more readily the most subtile. 

 Yet we find that these viscid secretions are even unmixed with the 

 thinner ones. Hence it is necessary to infer that the hydraulic 

 laws are superseded. 



22. If a fluid which is capable of passing freely through 

 tubuli is forcibly impelled against them (as with the impetus of 

 the circulation) and does not enter them, and if at the same time 

 these tubuli admit a grosser fluid, it is necessary to infer that they 

 admit the grosser fluid, by some agency of attraction, or affinity 

 which is more efficient than the force with which the thinner fluids 

 are impelled against their orifices. In this way, becoming filled 

 with the viscid, the more subtile fluids are excluded. 



23. This power of affinity or attraction we need scarcely in- 

 quire after. It is not exerted after death : it is peculiar to, we 

 may say without assuming too much, it is dependent upon, that 

 which distinguishes the living from the dead structure; it is de- 

 pendent upon the living spirit. With what properties or sub- 

 stances, or with what class of properties or substances, then exist- 

 ing in the blood, is this living spirit related? 



24. In answer to this question, it must be remarked, the pro- 

 ducts of the secreting function are found to consist of chymical 



