148 



EXCRETION. 



even fatal. The term used by the older phy- 

 siologists was excrementitious secretions. Some 

 general observations may be made on these ex- 

 cretions, with the view both of stating the pre- 

 sent extent of our knowledge on this mysterious 

 subject, and of pointing out the importance of 

 an arrangement and combination of facts re- 

 lating to it, which are usually treated, perhaps, 

 in too unconnected a manner, but the con- 

 nexion of which is already perceptible, and 

 can hardly fail to be satisfactorily elucidated 

 in the progress of physiology. 



When we shall have more precise informa- 

 tion as to the peculiar, and hitherto obscure 

 principles, which regulate the chemical changes 

 continually taking place in living bodies, it does 

 not seem unreasonable to anticipate, that a dis- 

 covery will be made, connecting the excretions 

 of the body with the assimilation of the food, 

 and with the nourishment of the different tex- 

 tures, a discoveiy which may be equally as 

 important in illustrating the chemical phenome- 

 na of the living body, as that of the circulation 

 was in explaining those changes which come 

 more immediately under our observation. In 

 the mean time, we can point out a great deal of 

 contrivance, connected with the general function 

 of excretion, and can state what are the general 

 injurious results, when this contrivance fails of 

 its intended effect; but we are unable to explain 

 how the contrivance effects its purpose, or to 

 point out any general law, by which these in- 

 jurious results are determined. 



I. We may state, in the first place, that the 

 necessity for some kind of excretion, or dis- 

 charge of certain matter from the organized 

 frame, corresponding to the acts of nutrition, 

 or of reception and assimilation of external 

 matter, is a law of vital action, applicable to all 

 organized beings without exception. The uni- 

 versality of the excretion of carbon, (whether 

 pure, or in the form of carbonic acid, we need 

 not now inquire,) has been established by the 

 inquiries of Mr. Ellis and others, and the poi- 

 sonous influence of the carbonic acid, in an un- 

 diluted state, to all living beings, is an equally 

 general fact. In all animals, which possess 

 organs of such size and distinctness as to make 

 their economy matter of observation, other excre- 

 tions are likewise observed; and in vegetables, 

 it is not only certain that various excretions, 

 besides the exhalation of water and of carbonic 

 acid, take place, but it is even believed by 

 De Candolle, that all the peculiar products 

 of vital action, excepting only gum, sugar, 

 starch, and lignine, (which have nearly the same 

 elementary composition, and are convertible 

 into one another,) and, perhaps, fixed oils, are 

 applied to no useful purpose in the economy, 

 and are poisonous to the plants in which they 

 are formed, if taken in by their roots and com- 

 bined with their sap ; so that, although often 

 long retained in individual portions of the 

 plants, they all possess the essential characters 

 of excretions.* And it appears to be well ascer- 

 tained by the observations of De Candolle and 

 of Macaire, that at least great part of the proper 



* Physiol. Veget. p. 217. 



juices of vegetables, which descend chiefly by 

 their bark, and are expelled into the soil, are 

 destined to excretion only, and are noxious to 

 plants of the same species, or even of the same 

 families, if growing in that soil (although often 

 useful to the growth of plants of different fami- 

 lies) ; and this principle has been happily ap- 

 plied by the former author to explain the neces- 

 sity of rotation of crops of different natural 

 families, to prevent deterioration of the produce.* 



As this necessity of excretion appears to be 

 so general an accompaniment of the vital action 

 of all organized beings, it seems obvious that 

 there must be some general law, which deter- 

 mines the noxious quality of these products of 

 that action, and imposes the necessity of their 

 expulsion. Yet it is certain that the chemi- 

 cal elements which pass off in the excretions, 

 are the same which are found in the textures of 

 the animal body, and in the nourishment, which 

 is essential to animal life. 



It would appear, therefore, that the noxious 

 property belongs to certain combinations only 

 of these elements, which are formed in the course 

 of the chemical changes in living beings, and 

 which, when once formed, must either be ex- 

 pelled from the body, or else laid up in cells 

 appropriated for the purpose, (as in the case of 

 the resins and volatile oils in vegetables, and of 

 the bile in the gall-bladder in animals,) and kept 

 out of the mass of the nourishing fluid. 



There is one general fact, on which much 

 stress has been justly laid by Dr. Prout, which 

 is confirmed by M. Raspail, and which may, 

 perhaps, be concerned in determining the 

 noxious qualities of certain compounds, in liv- 

 ing beings, viz. that although the elements 

 which enter into the composition of organized 

 bodies, readily combine, in other circumstances, 

 so as to form crystals, yet the peculiar combi- 

 nations which they form in all the textures 

 which are essential constituents of those organic 

 structures are never crystalline. When a crystal 

 occurs in an organized body, according to Dr. 

 Prout,-f- it is always either the result of disease, 

 or of some artificial process, or it is part of an 

 excretion, separated from the nourishing fluid 

 and from the useful textures.! Every one of 

 these textures contains, even in its minutest 

 particles, saline and earthy, as well as animal 

 or vegetable matter ; but the combinations are 

 always so arranged, by the powers of life, that 

 these saline and earthy particles are always dif- 

 fused through membranes, fibres, or cells, never 

 concentrated in crystals. On the other hand, 

 the elements constituting the peculiar matters of 

 the excretions are generally in such a state of 

 combination as readily to assume the crystalline 

 form, either alone, or in the simplest farther 

 combinations of which they are susceptible ; 

 and it seems possible, that this circumstance 

 may be part at least of the cause which necessi- 

 tates their expulsion. This is only matter of 



* Ibid. p. 249, and p. 1496. 



f Lectures in Medical Gazette, vol. viii. 



j "Jamaisje n'ai ape^u/' says Raspail, " de 

 cristaux dans le sein d'une cellule vivante et d'ac- 

 croisement," Raspail, Chimie Organique, 1378. 



Ibid. 1390. 



