SECRETION. 



459 



ceration of the intestinal glandulne, which is 

 so frequent a complication of fevers and of 

 other diseases induced by the presence of a 

 morbid poison in the blood, results from the 

 continued operation, upon their own structure, 

 of the noxious matter which these glandulre are 

 endeavouring to eliminate from the system. 

 This view has derived important confirma- 

 tion from experiments recently made by Prof. 

 Liebig ; these having indicated that the sub- 

 stances to which the faeces owe their peculiar 

 fetor may be artificially produced by the im- 

 perfect oxidation of albuminous compounds.* 

 The immense relief frequently given by an 

 attack of diarrhoea, which spontaneously eli- 

 minates morbific matters that were operating 

 prejudicially on the system, and the corre- 

 sponding effects of mild purgatives, which 

 excite the secreting action of these glandulae, 

 furnish additional evidence, if such be re- 

 quired, to the same effect. It is obviously 

 important in a therapeutic point of view, that 

 definite ideas should be entertained on this 

 subject ; and although it may be difficult to 

 obtain positive proof of the position here ad- 

 vanced, that it is the special function of the 

 glandulae of the lower part of the small intes- 

 tines, and at the upper part of the large, to 

 eliminate from the blood the putrescent 

 matter which results from the disintegration 

 of the tissues, it will scarely be denied that a 

 strong probability has been established by the 

 foregoing evidence, in favour of such a view. 



The interruption of any of these excreting 

 processes, by causing an accumulation of 

 effete matters in the blood, occasions speedy 

 death (see EXCRETION); and Dr. Marshall 

 Hall was perfectly correct in affirming f, that 

 the functions of egestion are more immediately 

 necessary to the maintenance of life than 

 those of ingcstion. For whilst most animals 

 may live for a considerable time without food, 

 and many without oxygen, there are none 

 which are not speedily killed (unless pre- 

 viously reduced to a state of torpidity) by 

 the complete suspension of the excretory 

 operations. 



In all the cases hitherto considered, the 

 necessity for the secreting function arises out 

 of the changes which are continually taking 

 place in the system at large, and which tend 

 to produce an injurious effect upon the cha- 

 racter of the blood. We have seen, however, 

 that even the act of liberation of effete or 

 superfluous matters is frequently made to 

 answer some ulterior purpose in the economy ; 

 and we are thus led to notice the other class 

 of secretions, in which this ulterior purpose 

 appears to be the principal, if not the sole, ob- 

 ject of their separation. The variety of these, 

 however, is so great, and their uses are so 

 different, that no general statement can be 

 made regarding them. It must suffice to re- 

 fer to a few examples, such as will show their 

 importance in the economy of the different 

 animals which form them. The secretion of 

 tears for the cleansing and lubrication of the 



* Animal Chemistry, 3d ed. p. 154. 

 t Gulstonian Lectures, 1842. 



surface of the eye ; the salivary, gastric, and 

 pancreatic secretions for the reduction and 

 solution of the food ; the mammary se- 

 cretion for the nutrition of the offspring; 

 the sebaceous secretions for the lubrication 

 of the skin ; the mucous secretions for 

 the protection of the mucous membranes ; 

 the poisonous secretions of certain serpents, 

 insects, &c. ; the glutinous secretion with 

 which the silkworm weaves its cocoon and 

 the spider its web ; the pigmentary secretion 

 of the cuttle-fish ; the colouring matter se- 

 creted by the mantle of many of the mollusca 

 for imparting various hues to their shells ; 

 the strongly odorous secretions of many ani- 

 mals, which seem generally attractive to those 

 of their own kind, but repulsive to others; 

 together with many others that might be 

 cited, are sufficient to indicate that the form- 

 ation of even a very small amount of some 

 peculiar product may be essential to the well- 

 being of the animal which furnishes it ; by 

 contributing to the due performance of one or 

 more of its vital functions, or by the protec- 

 tion it affords to some important organ. 



Existence of the elements of secretions in the 

 blood. The chemical proofs which have 

 been recently obtained of the presence of the 

 characteristic elements of certain secreted 

 fluids in healthy blood, have afforded the 

 most complete evidence of that which was 

 previously highly probable, namely, that the 

 office of the secreting organs is more that of 

 selection and separation than that of conver- 

 sion. The proof is most complete and satis- 

 factory in regard to the chief elements of the 

 urinary secretion ; but inferential evidence 

 scarcely less conclusive exists with regard to 

 several other substances. 



The presence of urea in the blood was first 

 clearly shown by Prevost and Dumas*, who 

 found that when the functions of the kidneys 

 were destroyed, either by the extirpation of 

 those organs, or by ligature of the renal ar- 

 teries, urea could be detected in the circula- 

 ting fluids after a short period. Similar re- 

 sults have been obtained by other experi- 

 menters ; and pathological observation, in 

 cases where the normal secretion has been 

 suspended or greatly diminished (as in the ad- 

 vanced stages of Bright's disease), has equally 

 shown that under such circumstances the 

 presence of urea manifests itself in the blood 

 when duly analysed.f An interesting case 

 has lately been put on record by Dr. Shear- 

 man, in which the secretion of true urine 

 being temporarily suspended, in consequence 

 of accident (a watery fluid, containing neither 

 urea, uric acid, nor the urates, being all that 

 was passed for some days), urea was ob- 

 tained in considerable quantity from the se- 

 rum of blood drawn from the arm.J It would 

 be difficult to explain such facts in any other 

 way, than by supposing that urea is con- 

 stantly being generated in the system, and 



* Annales de Chimie, torn, xxiii. 

 f See Christison in Edinb. Med. and Surg. Jouru. 

 18^9. 



% Edinb. Monthly Journal, March, 1848. 



