The cyclopaedia of practical medicine: comprising treatises on the nature and treatment of diseases, materia medica and therapeutics, medical jurisprudence, etc., etc (Volume 4).
- Date:
- 1845
Licence: Public Domain Mark
Credit: The cyclopaedia of practical medicine: comprising treatises on the nature and treatment of diseases, materia medica and therapeutics, medical jurisprudence, etc., etc (Volume 4). 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.)
14/804
![son Philip; ami, upon the whole, it is tolerably well ascertained that the temperature of the body sinks, if it be not maintained by the chemical changes which occur in respiration. But, notwithstanding the support thus given to Dr. Crawford's opinion, many and as strong facts have been advanced in support of that view of the subject which regards nervous energy as the source of animal heat. The most important ex- periments on this side of the question are those of Mr. [Sir B.] Brodie. He found that, by maintain- ing the action of the heart by artificial respiration after the brain is removed, although the blood undergoes its ordinary changes, yet that the tem- perature of the animal thus treated is rapidly lowered. Sir B. Brodie's experiments were made on rabbits, in which the functions of the brain were suspended by dividing the spinal marrow: the blood, in both systems, underwent no change different from that which occurs in natural res- piration. It may perhaps be urged, says Sir B. Brodie, that, in these experiments, the secre- tions had nearly, if not entirely, ceased : it is probable that the other changes which take place in the capillary vessels had ceased also, and that, although the action of the air on the blood might have been the same as under ordinary circum- stances, yet there might not have been the same alteration in the specific heat of the fluid as it flowed from the arteries into the veins. But, on this supposition, if the theory of Dr. Crawford be admitted as correct, there must have been a gradual but enormous accumulation of latent heat in the blood, which we cannot suppose to have taken place without its nature having been en- tirely altered. If the blood undergo the usual change in the capillary system of the lungs, it is probable that it must undergo the usual change in the capillary system of the greater circulation also, since these changes are obviously dependent on and connected with each other. From the '«xperiments of Sir B. Brodie it appears that, when the functions of the brain are suspended, ■the power of generating animal heat is also sus- ■pended ; although the same quantity of oxygen be consumed as in natural respiration under ordi- nary circumstances. It is, nevertheless, proper to mention here the opinion of M. Le Gallois, that, owing to the nature of artificial respiration, upon -which Sir B. Brodie's conclusions are founded, the temperature may fall, and the animal be killed by cold, although ever^ part remain uninjured. The air in artificial respiration does not enter the pulmonary cells in the same manner as in natural Tespiration, but is forcibly propelled into them ; a large formation of frothy mucus occurs, which both prevents the air coming in contact with the , lining membrane of the air-cells, and by its eva- poration tends to cool the body. Many other facts concur, also, to prove that the temperature of the body is regulated by the nervous energy. It is true that these demonstrate its effect chiefly in maintaining the heat of parts ; but if its influence on parts be admitted, it is not easy to conceive on what grounds its power over the entire system can be denied. Sir Everard Home divided the nerves going to the growing antler of a stag, and found that the temperature almost immediately fell; and although, after a few days, it rose again higher than before, yet this may have originated from the reunion of the divided nerves : at all events it does not invalidate the fact that the temperature fell on the division of the nerves, and, consequently, was regulated by their condition. In paralyzed limbs the tem- perature sinks, although in many cases the circu- lation in the limb is unaffected, and the paralysis is confined to the sensibility of the member. In a case recorded by Mr. Earle, in which the axil- lary plexus of nerves on one side was crushed, the paralyzed limb of that side was of a lower temperature than the opposite limb: indeed, in general we find that increased nervous action, whether depending on affections of the mind or on other causes, augments the heat of the body ; whilst the effect of depressing passions, which diminish nervous energy, is followed by either general chilliness, or coldness of the extremities. These facts undoubtedly go far to prove that animal heat is a vital principle closely connected with the integrity of the nervous system ; but at the same time, as the stimulus of arterial blood is requisite for the excitement of the brain and nerves, and arterialization is the result of respira- tion, the influence of respiration in the production of animal heat must be so far admitted; for with- out the function of the lungs the brain would lose its energy, and the temperature of the system be necessarily greatly lowered. This opinion re- ceives also considerable support from some ex- periments of Dulong to ascertain whether the quantity of caloric, developed by the consumption of oxygen in respiration, be equivalent to the quantity given out by the body. He found that in carnivorous animals the proportion is equal to forty-nine and fifty-five parts in one hundred of the heat generated by the whole body during the same interval of time; and, in phytivorous ani- mals, to betwixt sixty-five and seventy-five parts; and that the whole quantity of caloric and water together is equivalent to sixty and eighty parts only ; so that the animal heat is greater than can be accounted for by the fixation of oxygen during respiration. Upon the whole, the examination of both sides of the question leads us to conclude that both opinions are to a certain extent true ; that animal heat is influenced chiefly by the state of the nervous system, but partly, also, by the chemical changes which take place in the lungs during respiration. [See, on all this subject, the physiological works of Miiller, Carpenter or Dun- glison.] If this view of the sources of animal heat be correct, it presents a considerable obstacle to the admission of Dr. Murray's explanation of refrige- rants, which can only be regarded in the light of an ingenious hypothesis. The subject, therefore, remains as he found it; and the question presents itself—can no rational explanation of the opera- tion of refrigerants be suggested 1 The writer of this article, although he does not venture to offer a theory likely to be generally adopted, yet con- ceives that some approach to a rational explana- tion may be attained by ascertaining how far the action of refrigerants taken into the stomach re- sembles that produced on the skin by similar substances. In abstracting caloric from the surface of the](https://iiif.wellcomecollection.org/image/b21116799_0014.jp2/full/800%2C/0/default.jpg)
