EXCRETION. 



161 



liquides. Cette vesicule, par sa vitality proprc, 

 alisi irl inn- purtie (In fluidc qui 1'entourc ; 

 ce fluide est ou de 1'eau presque pure, et alors 

 elle en cst simplement impregnee et lubrifiee ; 

 ou de 1'eau plus ou moins chargee <le cette 

 matiere gommeuse, elalxin < dans Ic s feiiilles 

 ;t d'autres inalieres alimenUiires qui peuvent 

 se trouver nortecs avec hi seve duns li.'S diversrs 

 part it'.s. I. n i .-< 'static </ui I'n alinirbec lui Jait 

 tulnr unc action determinie ifaprtf sa propre 

 niitiin; et cette action modih'e les matenaux 

 contenus dans la cellule, de maniere a en faire, 

 ou 1'une des matieres communes que nous 

 avons considerees, ou 1'une des matieres que 

 nous aurons bieutot u examiner, telles que 

 les Imiles volatiles, les resines, &c. Certains 

 vaissraux analogues il la nature des cellules 

 joucnt le mimic role sous ce rapport. Les 

 matieres ainsi localement elabories peuvent, ou 

 rester dans les cellules ou les vaisseaux qui 

 leur ont domic naissance, ou s'extravaser au 

 dehors ct donner lieu, soil a des excretions, soil 

 & des transports des matieres d'une partie a 

 1'autre du tissu."* 



The description given by Dutrochet of the 

 act of secretion as it may almost be detected 

 in the glands of the lower classes of animals, 

 is exactly similar. " Entre les vesicules qui 

 composent le tissu organique des animaux 

 rampent les vaisseaux sanguins, chez les animaux 

 a circulation : ces vesicules sont appliqu^es 

 sur les parois des vaisseaux ; et il est certain 

 que la cavitd des vesicules ne communique 

 point immediatement avec la cavite des vais- 

 seaux, puisque le meme fluide n'existe point 

 dans leurs cavite's. Ce fait est trfcs facile a 

 verifier, en cxaminant au microscope It: tissu 

 d'un organe secretive chez uu mollusque gas- 

 teropode, celui de la foie par example : on 

 voit toutes les vesicules de cet organe remplies 

 par la bile, que 1'on distingue a sa couleur, 

 tandisque les vaisseaux sanguins qui cotoient 

 ces vesicules n'ont que la diaphanietd que leur 

 donne 1'etat incolore du sang qui les remplit. 

 Ainsi, les vaisseaux sanguins u'taistent que 

 com me des moyens d'irrigation pour les vesi- 

 cules qu'ils cotoient, et ce n'est peut-etre que 

 par filtration que le Huide sanguin p^netre, en 

 si modijiant, jusque dans ces vesicules elemen- 

 taires. Le systeme sanguin, considerc dans 

 son entier, forme une cavitt; sans issue, dans 

 laquelle rien ne peut entrer, et de laquelle rien 

 nc pent sortir, autrement que par filtration."^ 



Any one who is acquainted with the elabo- 

 rate " Vasorum Lymphaticorum Historia" of 

 Masragni, will recognize the perfect accordance 

 of this statement with the result of his cartful 

 and minute investigation of the structure of the 

 secreting organs in the higher animals. J 



We may consider, then, the act of secretion, 

 ' en deniicre analyse," as consisting simply in 



" Physiol. Vegetale, p. 215. 



t L 'agent immcdiat ilu mouvemcnt vital dcvoile. 

 &c. p. ]<ii. 



J It must not be considered as ascertained, that 

 the files or tracks of globules of blood seen under 

 the microscope, and usually called capillaries, 

 have really, in all animals, and all parts of these, 

 vascular coats. It seems pretty certain, that iu 



the passage of certain portions of a c<>ii>|niil 

 fluid through a thin living membranr, ami tin 

 exclusion of others; or, according to the for- 

 tunate expression of Dutrochet, us a du mind 

 filtration. " All that is necessary fur any 

 kind of secretion in a living animal,' says Mr. 

 Mayo, " is a vascular membrane, and all the 

 arrangements of the glands appear to be merely 

 t ontnvances for conveniently packing a great 

 extent of such a surface in a small compass." 

 And if we are asked, to what cause we can 

 ascribe this escape of certain matters from the 

 circulating fluid through one portion of mem- 

 brane, and of others through another, we can 

 only answer, in the words of this last author, 

 that it depends on the exercise of certain " vital 

 ajiiniliet, peculiar to the living state, anil the 

 existence of which will always be an ultimate 

 fact in Physiology, although we may attain to 

 a knowledge of the laws according to which 

 they o|>erate. 



V. One principle may already be laid down, 

 almost with certainty, as to the exercise of these 

 powers in the present instance, viz. that the 

 peculiar matters characterizing the excretions 

 are not actual \yformed from the blood at the 

 parts where they appear, but only separated 

 from the blood at these parts, their formation, 

 if not actually completed, having been at least 

 considerably advanced, in the blood itself 

 which reaches these parts. Of this we are 

 well assured, chiefly by the following facts. 



1. The experiments already mentioned, first 

 made by Prevost and Dumas, have proved 

 that within a short time after the extirpation of 

 the kidneys in animals, urea may be detected 

 in the blood, showing clearly that the existence 

 of these glands is not necessary to the forma- 

 tion of this very peculiar excrement itiotis matter, 

 and giving us reason to conjecture that the 

 office of the kidneys is, not to form the urea, 

 but to attract it out of the blood as fast as it is 

 formed there. The same existence of urea in 

 the blood has been ascertained in the human 

 body, both in cases of diseased kidneys, when 

 the excretion there was much impeded, and in 

 cases of malignant cholera, when the excretion 

 was suppressed. The cases of rapidly fetal jaun- 

 dice already mentioned, where the bile-ducts were 

 |>ervious and empty, would seem to have been 

 cases where the peculiar matter of the bile has 

 been in like manner formed in the blood, 

 without finding the usual vent at the liver. 

 And it will appear under the head of Respira- 

 tion, particularly from the experiments of Dr. 

 Edwards, and of Collard de Martigny, that 

 there is good reason to believe the carlnic acid 

 of expired air to be formed in the course of the 

 circulation, and only exchanged for oxygen at 

 the lungs. 



2. There are various instances in disease, of 

 substances generally found in the secretions of 

 certain glands only, being deposited in situa- 

 tions quite unusual, and where no textnrr 

 .similar to these glands exists ; e. g. cholesterine, 



many cases they are only lines or membranes, or 

 channels in a solid parenchyma ; but still the obser- 

 vation in the text applies strictly to the escape of 

 any particles of the circulating fluid from them. 



