152 



EXCRETION. 



which in the natural state is found only in the 

 bile, has been found deposited in diseased 

 structures in the brain, kidneys, pelvis, scro- 

 tum, &c. ; and lithic acid, naturally existing 

 only in the urine, is deposited in cases of chalk- 

 stone in the textures immediately surrounding 

 the joints of the fingers and toes. It seems to 

 be nearly in like manner that purulent matter, 

 when mixed in unusual quantity with the 

 blood, as by inflammation of a vein, is fre- 

 quently deposited in individual parts of the 

 body, with little or none of the usual sym- 

 ptoms, or of the other accompaniments, of in- 

 flammation at these parts. 



3. There are a considerable Dumber of cases 

 recorded on unexceptionable evidence, where 

 excretions have passed off per aliena cola, i. e. 

 by organs which in the natural state yield no 

 such products, and the structure of which is 

 widely different from that of the glands where 

 they are usually secreted. This has been most 

 frequently observed of the milk and of the 

 urine, and of the latter, both in cases where 

 the secretion at the kidneys had been sup- 



rsed, and in cases where its discharge by 

 urinary passages has been obstructed, so 

 as to occasion its re-absorption. In both cases 

 it is obvious that the peculiar matter of this 

 excretion must have been first mixed generally 

 with the blood, and then deposited in indivi- 

 dual parts of the system, widely different as well 

 as distant from those where it usually appears. 



In cases of this kind collected by Haller,* 

 the vicarious discharge of urine is stated to 

 have occurred from the skin, from the stomach, 

 from the intestines, and from the nipples ; and 

 in cases recorded by Dr. Arnold and Dr. Sen- 

 ter in America, it is stated to have been passed by 

 vomiting, by stool, from the nose and from the 

 mammae, as well as other parts .f Both in 

 cases given by Haller, and in one recorded in 

 Magendie's Journal de Physiologic, (vol. vii.) 

 milk is stated to have been evacuated in quan- 

 tity from pustules that formed on the thigh ; 

 and among the former are instances of its hav- 

 ing passed off" from the salivary glands, the 

 kidneys, and the uterus. Such statements 

 were formerly considered as fabulous, but since 

 the facts already mentioned (and particularly 

 the appearance of urea in the blood after ex- 

 tirpation of the kidneys) have been ascertained, 

 this scepticism seems no longer reasonable. 



It must be here observed, that the healthy 

 blood is easily shown to contain in itself mat- 

 ters more nearly akin to all the solid textures 

 and to the other secreted fluids of the body, 

 than to the bile and the urine ; and hence, if 

 we are satisfied that the elaboration of these 

 latter fluids is effected in the blood itself, and 

 does not essentially require any special action 

 of the organs in which they usually appear, 

 there can be little hesitation about extending 

 this inference to other acts of secretion and 

 to nutrition. It appears, therefore, at least 

 highly probable, that the whole processes of as- 

 similation and elaboration of the fluids in the 



* Elem. Phys. lib. vii. ch. 1. 



t London Med. and Phys. Journal, 1828. 



living body are carried on, as other chemical 

 changes on fluids are, in the interior of these 

 fluids themselves, and that the solids of the 

 body are concerned in these changes only in 

 two ways : Jirst, by securing the complete sub- 

 division and intimate intermixture of the fluids 

 necessary to their chemical changes ; and second- 

 ly, by determining the parts of the body where 

 peculiar matters, already existing in the blood, 

 shall be deposited from it, or attracted out of it. 



VI. We may next enquire, what is the most 

 probable original source of the matters which 

 are thrown out of the body in the way of ex- 

 cretion. As it is generally believed, and on 

 strong grounds, that the solid textures, as well 

 as prepared fluids of the body, are liable to 

 continual decay and renovation, it has long been 

 the general belief, that the materials for the ex- 

 cretions are supplied chiefly from those sub- 

 stances which have formed part of the textures, 

 and, after fulfilling their office there, have been 

 taken back into the circulation with a view to 

 their discharge from the body. And it has 

 been conjectured, certainly with much probabi- 

 lity, by Berzelius and by Autenrieth, that the 

 animal matters thus mixed with the blood on 

 their way to the excretories, are distinguishable 

 from the albuminous or nutritious parts of the 

 blood, by their solubility both in hot and cold 

 water, and constitute the animal matter of the 

 serosity, or uncoagulable animal matter of the 

 blood. This is supported by the observation, 

 that, when the kidneys are extirpated, this 

 part of the blood is first observed to increase 

 in amount, and afterwards it is here that the 

 urea is detected.* And the connexion of 

 the excretions with absorption from all parts of 

 the body seems farther illustrated by the pheno- 

 mena of diabetes, which may be held to be the 

 disease in which there is the strongest evidence 

 of increased absorption in all parts of the body, 

 from the rapid digestion, the rapid recurrence 

 of thirst after drinking, the dryness of the sur- 

 face, and the progressive emaciation notwith- 

 standing the excessive amount of ingesta ; and 

 in which the quantity of the urine is often ten 

 times, and the solid contents of the urine often 

 twenty times, the average quantity in health.f 



But it should not be too hastily concluded, 

 that all the solid constituents of the animal body 

 are liable to continual absorption and renova- 

 tion. The permanence of coloured marks on 

 the skin, noticed by Magendie, is sufficient 

 evidence, that, in some of the textures, any such 

 change must go on very slowly ; and some of 

 the best observers doubt whether any such pro- 

 cess of alternate deposition and absorption takes 

 place in vegetables, in which, nevertheless, as 

 we have seen, excretion is a necessary process. 



* Prevost et Dumas in Ann. de Chimie, t. xxiii. 

 p. 97. 



t The change of nature of the animal part of 

 this solid matter, (viz. the disappearance of part of 

 the urea, and substitution of an excessive quantity 

 of sugar,) is evidently connected with the singular 

 fact ascertained by Dr. Prout, that sugar differs 

 from urea simply in containing no azote, and a dou- 

 ble quantity of carbon and oxygen : a discovery 

 which will, probably, acquire a greatly increased 

 importance in the progress of organic chemistry. 



