Page:The American Cyclopædia (1879) Volume I.djvu/554

 522 ANIMAL HEAT crackling sparks passing from his scalp. But it is in the United States that the most interest- ing fact concerning the production of static elec- tricity has been observed. It was in a lady, who for many months was in an electrical state so different from that of surrounding bodies, that, whenever she was but slightly insulated by a carpet or other non-conducting medium, sparks would pass between her per- son and any object she approached; when she was most favorably circumstanced, four sparks per minute would pass from her finger to the brass ball of the stove at the distance of 1 inch. Sometimes the electricity thus devel- oped is sufficient to light the gas from an ordi- nary burner. From the pain which accompa- nied the passage of the sparks, the lady's con- dition was a source of much discomfort to her. The circumstances which appeared most favor- able to the production of electricity were an atmosphere of 80 F., tranquillity of mind, and social enjoyment; while alow temperature and depressing emotions diminished it in a corre- sponding degree. The phenomenon was first noticed during the occurrence of an aurora borealis; and though its appearance was sud- den, its departure was gradual. Articles of dress had no influence upon its intensity. ANIMAL HEAT, the heat produced in the in- terior of animal bodies by the nutritive changes going on in the blood and the tissues. Living animals, as a general rule, if not invariably, have the power of generating heat within their own bodies. The proof of this is, that in many of them the temperature of the body is habit- ually above that of the surrounding atmos- phere or water in which they live. Thus the temperature of the porpoise has been found to be 99-5 F., and that of the seal 104. The temperature of the human body, and that of the quadrupeds generally, is about 100 ; while that of many of the birds is 105, 110, or even 111. As this temperature is maintained at or about the same standard, though that of the external atmosphere may be much lower, and as the animal is consequently losing heat in- cessantly by radiation and conduction, it is evident that there is a constant supply from an internal source by which the external loss is made good. In man and in all the higher ani- mals, namely, birds and mammals, this internal heat is very active; so much so that their higher temperature is easily distinguished both by the touch and the thermometer, and is kept at almost a uniform standard whatever may be the external variations. These are therefore called the warm-blooded animals. In reptiles and fishes, on the other hand, the production of heat is less active ; their temperature is ha- bitually lower than our own, so that they feel cool to he touch ; and it varies so little from that of tSie surrounding media that greater care is requisite to distinguish it, even by the thermometer. ' They are accordingly distin- guished as the cold-blooded animals. Animal heat is generated, however, even in these species, as is demonstrated by exact observa- tion. Thus the temperature of a frog has been found to be 48 when immersed in water at 44-4 ; that of a serpent 88-4, in air at 81-5 ; that of a tortoise 84, in air at 79'5 ; and that of a fish from 1-7 to 2-5 above that of the surrounding water. In the invertebrate ani- mals, the appreciation of their temperature by the thermometer has been found more difficult, since, on account of their small size, the radiat- ing external surface is greater in proportion to the mass of heat-producing tissue within ; and the heat thus generated is almost as rap- idly dissipated. This difficulty, however, has been overcome in the case of insects by ex- perimenting upon a large number collected in a small space. Thus Mr. Newport found that when the temperature of the external atmos- phere was 34'5, that of the interior of a hive of bees was 48-5 ; and that if the insects were thrown into a state of active excitement by rapping on the hive, it would rise to 102. The heat thus produced in the interior of the body is not exactly the same in degree in every part. It is generated either in the blood itself or in the substance of the internal organs, or most probably in both. At all events, the blood acquires during its circulation through different organs slightly different degrees of warmth. Thus Claude Bernard has found, by introducing the bulb of a delicate thermometer into the vessels of a living dog, that the tem- perature of the blood in the abdominal aorta varied from 99 - 5 to 105'6 ; in the portal vein, from 100 to 106 ; and in the hepatic vein, from 101 to 106-8. The wannest blood in the body, on the average, was that of the he- patic vein, which had passed through two suc- cessive capillary circulations, namely, that of the intestines and that of the liver, since leav- ing the arterial system. On the other hand, while passing through an organ in which it is exposed to the influence of air and evapora- tion, the blood diminishes somewhat in tem- perature. Thus, in passing through the lungs it was found to have lost sometimes a little less and sometimes a little more than ^ F. For the same reason, the temperature of the skin is habitually a little lower than that of the internal organs. If the bulb of a thermo- meter be taken between the fingers of the closed hand, it will rise only to 90 or 95 ; in the axilla, carefully protected from the air, it will stand at 98 ; while under the tongue, and in contact only with the vascular mucous membrane, it will reach 100. In the external parts of the body, therefore, which are espe- cially exposed to the influence of the outer air, the temperature may vary considerably. Espe- cially the thinner parts, with a comparatively greater extent of surface, feel this variation in a marked degree, and may thus be affected with a local depression of temperature. On a very cold day the ends of the fingers, the nose, the ears, &c., may be cooled down very con- siderably, and in some instances may be even