ANIMAL HEAT. 



655 



internal parts to be pretty constant in the 

 normal state, the temperature of the right ven- 

 tricle of the heart and of the rectum may be 

 determined by taking the temperature of the 

 closed mouth ; that of the left ventricle will be 

 found by adding 0,44 c., or 1 F., to the degree 

 indicated. 



Relations in point of temperature between 

 external parts. We have only data for insti- 

 tuting comparisons in regard to the hand, 

 the axilla, the groin, and the feet among the 

 external parts of the body. In a moderate 

 summer-heat the hand appears to be the part 

 which is most susceptible of showing a high, 

 the feet the parts most susceptible of exhibiting 

 a low temperature. The axilla and groin gene- 

 rally exhibit nearly the same degree of tempe- 

 rature; and the amount in which they differ in 

 this particular from the mouth may be stated at 

 about 1, 75. 



When we direct our inquiries with a view to 

 ascertaining any general relation in the tempe- 

 ratures of different parts of the body, whether 

 external or internal, we soon discover, as has 

 been already stated, that this has no connexion 

 of an inverse kind with their distance from the 

 heart. At the same time there is a general 

 condition discovered influencing the tempera- 

 ture of the different parts. This is their situa- 

 tion in reference to the surface or inside of the 

 body. The temperature is higher, for instance, 

 within the trunk than on its outside. What- 

 ever other reason may be assigned for this, 

 there is one which is purely physical, that must 

 influence it powerfully. It is obvious that the 

 surface of the body and limbs must cool much 

 more rapidly than the interior of the body. So 

 that, supposing the temperature at first to be 

 every where uniform, the difference in the rate 

 of cooling would very soon suffice to cause a 

 notable reduction on the exterior beyond that 

 which took place in the interior of the body. 

 This cause, however, can only be charged with 

 its own share of influence ; there are others 

 which must act with considerable effect, and 

 among these especially the one upon which the 

 production of heat depends. We have seen 

 that the condition of the functions of nutrition 

 most closely in relation with animal heat was 

 connected with the arterial blood. Now inas- 

 much as the arterial blood is that which is most 

 intimately connected with the production of 

 caloric among animals, we might fairly expect 

 that the temperature generally would be rather 

 above that of the venous blood. And we have 

 seen that there was actually a difference be- 

 tween the temperatures of the two ventricles, 

 that of the left being the higher. Experiment 

 has also shown that there was a corresponding 

 difference in the temperatures of the two kinds 

 of blood circulating in the arteries and veins ; 

 arterial blood is actually higher in temperature 

 than venous blood to the extent of a degree of 

 Fahrenheit's scale. We shall add here, and in 

 conformity with the same principle, that it is 

 to this difference of temperature of the two 

 kinds of blood that the difference in the tempe- 

 rature of the right and left ventricle of the heart 

 is owing. We need not be hindered in adopt- 



ing this conclusion from the circumstance of 

 the blood of either ventricle being found in a 

 slight degree inferior in temperature to the ven- 

 tricle itself, inasmuch as the blood abstracted 

 from the canals that contain it, and exposed to 

 the air, begins to evaporate, and loses heat ra- 

 pidly. Nevertheless it is not demonstrated 

 that the difference in temperature of the blood 

 out of and of the blood in the ventricles of the 

 heart depends on this cause. There may be 

 another at work; the influence of muscular 

 contraction for instance, a point which we shall 

 examine generally by-and-bye. New means of 

 estimating variations of temperature have been 

 lately discovered, by which changes that en- 

 tirely escaped us as judged of by the thermo- 

 meter are made abundantly obvious; by which, 

 indeed, the temperature of parts inaccessible in 

 their natural and normal condition to the ther- 

 mometer are now investigated without diffi- 

 culty. In using the thermometer as the means 

 of estimating temperature, it is evident that 

 this instrument could not be introduced into 

 the external parts without injuring the tissues, 

 without incisions, &c., which would necessarily 

 alter them materially, and produce so much dis- 

 turbance in their functions, that an increase or 

 diminution of temperature must almost neces- 

 sarily have been the consequence. The ther- 

 mometer, besides, however small its dimen- 

 sions, has the inconvenience of always either 

 absorbing or giving out a considerable quantity 

 of heat according to circumstances, before it 

 gets into equilibrium with the parts with which 

 it is brought into contact. A necessary fall or 

 rise in the absolute temperature of these parts 

 is the natural consequence of this. Further, 

 the thermometer is incapable of showing sudden 

 variations in temperature; several minutes must 

 always elapse before it gets into a state of equi- 

 librium in regard to temperature with the parts 

 or medium surrounding it. If a thermometer, 

 for instance, be placed in the mouth, three or 

 four minutes must elapse before it will cease to 

 show any increase of temperature. Now if any 

 calorific phenomena of short duration were de- 

 veloped in that time, it is evident that all idea 

 of their occurrence would escape us. 



These considerations led to the adoption of 

 thermo-electrical means by Messrs. Becquerel 

 and Breschet. The processes they employed 

 in procuring indications of temperature were 

 the following. The only means we have of pe- 

 netrating into the interior of organs without in- 

 jury is to make use of a needle similar to that 

 employed in acupuncture. Now it is easy to 

 arrange this needle so as to obtain thermo-elec- 

 tric indications, which proclaim immediately 

 and with the greatest precision the temperature 

 of the part or medium with which the point 

 happens to be in contact. It is enough to 

 compose this needle of two others in metal, 

 two of the extremities of which are soldered 

 together in a few points only, whilst the other 

 two are placed in communication with one of 

 the extremities of the wire of an excellent ther- 

 mo-electric multiplier. The slightest changes 

 of temperature at the points of junction give 

 origin to an electrical current, which, in reacting 



