GLAND. 



lion. The former of thefe proce/Tes is nutrition or affimila- 

 tion ; the latter fecretion : they refcmble each other in their 

 commencement, in which the organ, by feme powers of a 

 nature entirely unknown to us, but peculiar to hving bodies, 

 and forming part of that complicated notion, which we ex- 

 prefs by the term vitality, feledts from the blood fuch prin- 

 ciples as fuit its nature or funftions ; but they differ in the 

 employment of what is thus felccled, which is retained in 

 the body, and afiimilated to the already exifting organiza- 

 tion in the fonner calc, and apphed to fome other purpofe in 

 the latter. The fubjeA of nutrition does not come under 

 our jioticeat prefent. 



The produils of iecretion rcfult from an effential change 

 in the compound conveyed to the organ, from a new combi- 

 nation of the principles contained in the blood, which is 

 transformed by the fpecific aclicii of the various organs into 

 different fluids, retained in or expelled from the body, ac- 

 cording to the qualities ef each. Hence, there are organs 

 which, after forming certain lluids, colleft and retain them; 

 while others feparate and expel their fecretions from the 

 body. The object of the fecretions is, to colledl thofe which 

 are deftined to fulfd important ufes in the body; while that 

 of tlie excretions is, on the contrary, to expel matters which 

 would be injurious to the frame. The two lunftions then of 

 fecretion and excretion refembl^ each other in moft refpecls : 

 there is in both a leparation and colleftioii of fluids. The 

 difference conUlts in this, that in the former cafe the fepa- 

 rated fluid remains in the body, while it is foon expelled in 

 the fecond. Thus fecretion always precedes excretion ; and, 

 in order to underftand the latter, it is neceflaiy to know how 

 the former takes place. 



The word fecretion, derived from fecerno, I feparate, 

 fignjfies fimpiy the adl of feparating; and its phyfiological 

 import is conveyed in that notion. It denotes, in phyfiology, 

 that funition of a living body, in which various fluids, dif- 

 fering from the blood and from each other, are prepared 

 from the common mafs of the blood, the fame fluid being 

 conftantly formed in the fame organ. No part of phyfiology 

 is more obfcure, and more difEcult in its invelligation, than 

 this very funftion. Malpighi, who had bellowed great 

 labour on the ilruclure of the glands, and was confidered to 

 have imveiled, in a great mealure, the myfteries of their or- 

 ganization, confefles his ignorance on this fubjeft; and, as 

 the avowal, from fuch a quarter, is interefting, we fubjoin 

 the paffage, obferving that the remarks here made, concern- 

 ing the kidnies, apply equaUy to all other fecretions. He 

 fays of the urinary fecretion, " quanam arte id contingat 

 obfcuriflimum : licet enim glandiilarum minifterio totum hoc 

 fubfequi rationi fit confonum, quoniam tarr.cn minima ilia, 

 fimplexque meatuum in glard dis ftruftura nos latet, ideo 

 qujedam tantum meditari pofu nus, ut huic quxfito proba- 

 biliter fatisfaciamus. Necefle eit hanc machinam interna con- 

 figuratione feparationis opus peragere; an vero his, quas ad 

 humanos ufus paflim ufiirpamus, quibus fere confimilia effigi- 

 mus, confonet, dubium; li.et enim occurrant analogs fpon- 

 gix, incerniculi, nitiilarum cribrorumque llruiturse, cui ta- 

 men ex his confiniihs undequaque fit retium fabrica, difficilli- 

 mum eft affignare, et cum naturx operandi indullria fecun- 

 diiSma fit, ejufdem igtiotse nobis reperientur machinae, et quas 

 nee mente quidem aifequi licet. Illud miror tarn copiofa, 

 diverfaque corpora feparari per has glandalas in nature ll:;lu, 

 exit enim fubiiantia aquea cum falinis, fulpiuireis et confi- 

 milibus particulis, et ex morbo etiam abfceffuum reliquii, 

 et totius qiiandeque corporis inqiiinamenta fcparantur de- 

 tentis fanguineis particulis," ^c De Vifcerum Struftura; 

 De Rciiibus, cap. 6. The whole bufinefs is carried on in the 



minute, and, as we may call them, elementary parts of the 

 vifcera and glands, the flrufture of which eludes the re- 

 fearch of our fenfes, and can ftill Icfs be developed by rea- 

 fonirg or refleftion. Obfervation cannot follow the work 

 throughout ; nor does it admit of elucidation by experiment, 

 like fome other fubjefts which have been explained by arti! 

 ficial imitation of the proceedings of nature. 



Unwilling to confefs their ignorance and leave their fyf. 

 terns imperfea, phyfiologifts kave attempted to raife, on 

 hypothefes, that ftrufture, for which anatomy afforded no 

 foundation. Their notions, refting merely on probabilities 

 and loofe analogies, have flouril}ied and fallen in fucceflion; 

 and we fliall find that the lift of truths and afccrtaincd fads 

 is much fliorter than that of opinions and errors. 



The compoGtion of the fecreted fluids prefents various 

 differences in the nature and proportions of their co.'^ftituent 

 parts. They poffefs, in common, all the general characters 

 which belong to animal fubftances: but each has certain 

 particular diftindive qualities, depending on the various fim- 

 ple or compound principles, the union of which determines 

 its fpecific nature. Thus, fetting afide the reilmblance of 

 ail our fluids, confidered as animal productions, fat does not 

 refemble bile ; the latter is very different from milk ; which, 

 again, has no refemblance to the falivary, gattrie, pancreatic, , 

 feminal fluids, &c. which mull be referred to fo many dif- - 

 ferent claffes. 



The arrangement of the animal fluids is more difScult 

 than we fliould have expeded at flrft fight. The falfe and 

 imperfect notions, which were long entertained of their chc- • 

 mical compofition, lead to claflifications founded on the 

 ufes to which they feemed to be deftined. Thofe employ- - 

 ed in the nourifhment and growth of the body were called 

 recrementitious, fuch as chyle, blood, ferum, lymph, &c. 

 The excrcmentitious included thofe which are expelled from 

 the body; as the urine, perfpiration, &:c. A third clafs 

 was made up of fuch as partake of the charadcrs of both • 

 thefe; of which a part is rejetted as noxious, while the reft 

 is retained, in order to anfwer fome particular purpofe. 

 Under the head of excremento-recrementitious humours, 

 were arranged the faliva, bile, pancreatic juice, mucus of ; 

 the inteftines, &c. The objeflions to fuch an arrangement 

 are too obvious to need enumeration. This divificn, as well 

 as that before alluded to, of excretions and fecretions, can- 

 not be adopted with any benefit, wliile the nature and ob- 

 jcits of many fecretions are fo httle underftood, that we can- 

 not determine whether they are expelled as noxious, or ferve 

 very ufeful purpofes in the economy. The bile, for ex^'- 

 ample, has been very commonly deemed an excrcmentitious 

 fluid, but by a completely arbitrary affumption: what proof 

 have we that perlpiration fcparates any thing noxious from 

 the blood ? For what reafon is the fecretion of the pancreas 

 placed in one rather than in the other of thefe divi- 

 fions? 



Pitcaime, who ivas followed by Michelotti, divided the 

 animal fecretions in a manner which has, at icait, the merit ' 

 of fimplicity, and loads to no falfe notions concerning their 

 ufes ; he dillinguifhed them merely as being thick or 

 thin. 



Haller diftributed the fluids into four claffes, according 

 to the chemical notions of his time, and to the degree of 

 complication in their elements, i. The aqueous fluids. . 

 Thofe have a very Lirge proportion of water in their com- - 

 pofition ; hence they are diilinguiihcd by their fluidity, and 

 have no ropinefs. Fire diffipates them almoft entirely, ex- 

 cepting a very fmall proportion of earthy refidue; neither 

 alcohol nor adds coagulate them, BefiJes a iilth- larth, - 



they 



