Defence of the doctrine of vital affinity / by William Pulteney Alison.

  • Alison, William Pulteney, 1790-1859.
Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: Defence of the doctrine of vital affinity / by William Pulteney Alison. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    11/18 (page 393)
    still farther diminished from their alternate contraction from the stimulus of the blood. There can be no doubt that in compounds the force of attraction subsist- ing among their constituent particles, is modified by the distance at which these are placed; and in compounds especially, which consist of four or more prin- ciples, the slightest alteration in their relative situation is sufficient to change entirely their existing attraction, and induce new combinations. The blood is a compound of this kind ; its ultimate principles, too, are capable of entering into an innumerable variety of combinations with each other; we may conceive, therefore, that when subjected to the contraction of the extremely minute vessels through which it is forced to circulate, the relative position of its elements will be changed, and new combinations formed. And if we suppose a fluid thus passing through tubes of different diameters, and undergoing successive decompositions, we may easily conceive that very different products may be formed from the same original compound. This affords a very simple view of the nature of Secre- tion. No complicated apparatus is requisite ; all that is necessary being the pro- pulsion of the blood through extremely minute vessels capable of contraction. And it is easy to account for the variations to which secretion is liable, as the contraction of the vessels must vary from variations in the state of their irritabi- lity and of the stimuli acting on them.” [Murray's System of Chemistry, vol. iv., p. 518.] In regard to the Nutrition of solids, Dr Murray says merely that they appear to attract immediately from the blood the materials which it contains ready formed, as there is probably “ no solid in the animal body, of which the imme- diate principles do not exist in the blood.” {Ibid., p. 516.] But I need hardly say that subsequent researches have not only completely demonstrated the insuf- ficiency of this explanation, but have shewn that the cause of the difference of products formed apparently from the same blood must be essentially different from that here assigned; and I would say farther, have shewn that the pecu- liarity of the compounds formed in living bodies cannot be reasonably ascribed to any modification of those movements of fluids, which Dr Daubeny regards as the only results of the vital principle. To shew this, I need not go into the question of the mode of action of arteries on the blood, or the portion of the changes essen- tial to secretion, which takes place in cells, exterior to vessels, and, of course, can- not be ascribed merely to the pressure to which the blood passing along the vessels may have been subjected; which had certainly been misapprehended by Murray, as by most other physiologists of that day. It is sufficient to quote a brief state- ment from Cuvier, which seems to me quite conclusive as to the question, whether difference of secreted fluids in the animal economy can be ascribed to difference in the structure of, and therefore of the movement of the blood through, the organs in which they appear. “ The same organ,” he says, i.e., the organ secreting the same fluid from the blood, “ presents in different classes of animals, sometimes in the same class, perfectly distinct structures. This is true of the 5 o