52 APPENDIX. 



IV. Of Pulmonary Transpiration. The mucus membrane of the lungs gives oft' a 

 considerable portion of the watery secretion, which is carried out of the lungs, in the 

 form of vapour, by the respired air. This perspiration equally takes place when the 

 animal breathes a gas containing neither oxygen, hydrogen, nor azote ; it, therefore, 

 does not result from the combining in the lungs of the hydrogen contained in the 

 blood with the respired air, but is strictly an aqueous vapour slightly charged with ani- 

 mal matter and is the production of a vital transpiration or secretion. 



It has not been determined whether or no it be produced from the bronchial, or from 

 the pulmonary arteries. The question is difficult to decide, as an injection thrown in- 

 to either set of arteries arrives on the surface of the air-cells. Pulmonary transpiration 

 may contain, like secretions, foreign matters which have been conveyed into the circu- 

 lation ; the lungs acting as an organ eliminating them from the system. This has been 

 shown by some experiments of Magendie, and also in an experiment which we per- 

 formed, in which ten drachms of the oil of turpentine were chiefly discharged by the 

 lungs, from the circulation in the state of vapour, within twenty-four hours. The 

 large quantity of the turpentine vapour evolved from the lungs on that occasion, leads 

 us to suppose that transpiration takes place principally from the venous blood about 

 the time when the changes are affected in it by respiration. This experiment, alst* 

 seems to support the doctrine of the evolution of carbon from the blood. 



Of the Production of Jlnimal Heat. 



4 



Note Y. 



It ia not necessary to add at this place, much to what is contained in the text. We 

 then attributed the production of animal heat to the vital influence exerted by that 

 part of the ganglial system distributed to the arteries on the blood which they circu- 

 late. 



Preparatory changes, however, take place in the lungs which are necessary to the 

 exertion of this influence, and to the evolution of heat ; but as it was contended tkat 

 those changes are more of a vital than of a chemical nature, so it is considered, that the 

 production of heat is more the result of the influence which the nerves of the vessels 

 exert upon the blood than of the change in the capacity for caloric which the blood 

 itself experiences in its passage into the venous state. The difference of capacity 

 which actually exists between venous and arterial blood is not sufficient, according to 

 the experiments of Dr. Davy, to form the basis of the chemical theory formerly re- 

 ceived, but the difference which actually does exist may be concerned in a subordinate 

 manner in the process. 



Conformably with the opinion, as was first maintained on an occasion already allu- 

 ded to, we infer that the various causes which modify the production of animal heat, 

 act, 1st. immediately upon the organic system of nerves themselves, changing the con- 

 dition of their influence ; 2d, upon the blood, altering the nature and composition of 

 this fluid, and thereby rendering it unfit for producing the requisite excitement of this 

 system of nerves, and incapable of the changes which the influence of these nerves 

 produces upon its constituent parts , 3d, immediately through the cerebro-spinal sys- 

 tem, modifying the influence which this system imparts to the ganglial. 



These different ways in which the vital influence, exerted by this system of nerves 

 in the production of animal heat, is modified, might have been illustrated by experi- 

 ments, and by reference to facts in comparative physiology and in pathology, if our 

 limits could have admitted of so great an extension of them. From what we have said 

 it will be perceived, that we view the production of animal heat more in the light of a 

 vital secretion than of a chemical phenomenon ; and that, like the other secretions and 

 nutrition, it proceeds from and is controlled by the vital influence of the ganglial sys- 

 tem of nerves. 



