It is impossible to carry the comparison further; the phenomena connected with heat in the lower grades of the animal creation become inappreciable; and this even in virtue of the same principle that has been an nounced; for the tissues are found to become more and more watery as we descend in the scale, till at length the solid constituent is almost inappreciable. Of course the circulating fluid must be watery in a still greater ratio; it contains but few globules; and then the ner vous system falls off in a still greaterpropor tion; it becomes more and more imperfect, till at length no trace of it is to be discovered. We thus arrive at the last links of the chain, after having run over the whole animal king dom, and we have found one uniform principle of correspondence between organic modification and calorific power. It were difficult to imagine any more satisfactory proof of a principle than has been afforded ; indeed as this has on no one occasion been found belied, we are fully authorized to regard it as established.
We have as yet examined but two points in reference to animal heat; 1st, the temperature of man and of the different classes of animals; 2d, the general relations of organization with the production of heat. In mentioning the temperature in any case, we have spoken of it as determinate; and farther, to have data that should be always comparable, the tempe ratures have been taken regularly in the same places,—viz. the mouth in man, and the other extremity of the intestinal canal in animals. We have still to ascertain whether the tempera ture varies or is identical in different parts of the body.
Temperature of different parts of the body.
—There is no need of the thermometer to tell us that all parts of the body do not at all times preserve the same temperature. NVe are often certain that the extremities are colder than the trunk for example; and a law of decrease of temperature in the ratio of the dis tance of parts from the heart had even been deduced from this observation. Hut when exact measurements came to be taken, this law was soon found to be at fault, as will he seen by-and-by in the course of these observations. Dr. Davy, in taking the temperature of the different parts of the body of a lamb, found that of the right ventricle of the heart 40°, 5 F.), that of the left ventricle 1 (106° F.). The left ventricle was therefore higher in temperature than the right to the extent of a degree of the scale of Fahrenheit's thermometer.
The temperature of the rectum corresponded with that of the right ventricle.
In my inquiries along with M. Gentil into the relations in point of temperature of certain external parts, we found in a strong man, perfectly at rest in mind and body, in the month of July, the external air being at 25 c. F.), the temperature of the month 38°, 75 F.) ; that of the rectum corresponded. The hands presented the next highest degree, marking nearly 37°, 5 5 F.). What is remarkable is that the axillw and groins, which corresponded with one another, were very sensibly lower in temperature than the hands; they did not raise the thermometer higher than 36°, 9G e. F.). The cheeks marked 93 5 F.), the temperature being ascertained by enveloping the bulb of the thermometer in the skin of these parts. The feet were a little lower, 62 (about 96° F.); their temperature being deter mined by placing the thermometer between the two, so that the bulb was surrounded on every side. The temperature of the feet was, there fore, notably lower than that of the hands, differing to the extent of 88 of the centigrade scale (above of Fahrenheit's thermometer). Placed on the skin between the thorax and abdomen the thermometer was at its minimum, not rising higher there than 35° (95° F.); but here a part of the bulb being in contact with the air, there must have been considerable cooling.
As the question here is not of absolute hut merely of relative temperatures, we can make great use of the results come to by the different writers quoted. We shall present a summary of these under the following head.
Relations between the temperature of inter nal parts.—lst. The warmest part of the body, according to John lIunter, is in the abdomen close to the diaphragm. 2d. The next part in point of temperature is the left ventricle of the heart. 3d. The right ventricle of the heart is the next in succession. The rectum and the mouth shut are of the same temperature. The greatest difference consequently between the temperature of these internal parts does not amount to more than centigrade, or at the utmost 2° Fahrenheit.
Supposing the relations in temperature of the 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.