Respiration subservient to nutrition : a thesis presented to the medical faculty of Harvard University, March 1850 / by E. Leigh.

  • Leigh, Edwin.
Date:
1853
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Licence: Public Domain Mark

Credit: Respiration subservient to nutrition : a thesis presented to the medical faculty of Harvard University, March 1850 / by E. Leigh. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    aid of respiration, their chyle is not fitted for assimilation, until after this indispensable function of respiration has intervened ; while, in the lowest class, even the chyme requires to be subjected to the influence of oxy- gen before it is perfectly adapted to the nutrition of the body. In all animals, therefore, the nutrient fluid, be it blood, chyle or chyme, must be aerated before it can be assimilated. Physiologists have hitherto supposed that this aeration of the blood has principal reference to the maintenance of a due degree of animal heat. With this, the decarbonization of the blood has been connected as subsidiary to it, or as also having an importance of its own in purifying the blood of a poisonous element. One or both of these offices of res- piration have been insisted upon as constituting the essence of this func- tion, and have been discussed at great length. The relation of the res- piratory function to nutrition has either been overlooked, or barely men- tioned, or, at most, briefly and doubtfully discussed. This is unques- tionably in a great measure owing to the fact, that in this, as well as in other departments, physiology has been studied with exclusive reference to the human system, or with some occasional references to other verte- brated animals, all of whom circulate blood containing red corpuscles. Tt is only in a few rare and more recent instances that comparisons have been freely extended into the inferior divisions of the animal kingdom. But certainly there can be no reasonable objection to going to the invertebratcd animals for light upon this or any other question in human physiology. On the contrary, such extensive comparisons are of the ut- most importance and will lead to the most valuable results. It is true, that their plan of structure is entirely different, that there is no ho- mology whatever between them and the highest type to which man be- longs. It has been satisfactorily shown that each of the four great di- visions has its own peculiar plan of structure, having, in this respect, nothing in common with the others. So that, while we may compare the legs, wings and fins, of the various classes of vertebrata with each other with reference to the plan of structure, we cannot make the least comparison, in this point of view, beyond the limits of each great division; we cannot compare the feet of man, of insects and of star- fishes, with each other. Still less can we compare the wing of a bird with the wing of an insect, the former being a modified leg or arm, the latter being a modified lung. So the penis of a lobster is a modified leg, which is not the case in any vertebrated animal. And the eye of a crus- tacean corresponds homologically to the end of his claw, but the eye of man cannot be in any way compared to the tip of his finger. So that the plan of structure of each great division is peculiar to itself, and