49 



HEART" S-EASE. 



HEAT, ANIMAL. 



they may be watched with greater precision. Soon after the septum 

 of the ventricles begins to be formed in the interior a corresponding 

 notch appears on the exterior, which as it gradually deepens renders 

 the apex of the heart double. This notch between the right and left 

 ventricles continues to become deeper until about the eighth week in 

 the human embryo, when the two ventricles are quite separated from 

 one another except at their bases ; this fact is very interesting from 

 its relation with the similar permanent form of the Dugong. At this 

 period the internal septum is still imperfect, so that the ventricular 

 cavities communicate with each other, as in the chick on the fourth 

 day. After the eighth week however the septum is complete, so that 

 the cavities are entirely insulated; whilst at the same time their 

 external walls become more connected towards their bases, and the 

 notch between them is diminished; and at the end of the third 

 month the ventricles are very little separated from one another, 

 though the place where the notch previously existed is still strongly 

 marked." 



We may now finally trace the distribution of the arterial trunks to 

 their final modifications, by which the creature is enabled to become 

 an air-breathing animal. The first, second, and third branchial arches 

 are replaced by the brachial and carotid arteries, and loose all commu- 

 nication with the primitive arterial trunk except at its commencement, 

 when the third pair of arches arises with the other trunks from its 

 dilated bulb. This remains as a single cavity even after the ventricles 

 have been separated. About the fifth or sixth day the bulb in the 

 chick becomes flattened, and its opposite sides adhere together, so as 

 to form two tubes running side by side; one of which unites with the 

 left, the other with the right ventricle. The one on the left becomes 

 the ascending aorta, that on the right the pulmonary artery. 



A knowledge of the changes which go on in the development of the 

 heart enables us to explain some of the malformations to which it is 

 subject. For an account of these see CYANOSIS; and HEART, DISEASKS 

 of, in the ARTS AND Sc. D:v. For further information on subjects 

 connected with the structure and functions of the heart, see ARTERY ; 

 CAPILLARY VESSELS; BLOOD; BLOOD-VESSELS; VEIN; HEAT, ANIMAL ; 

 RESPIRATION ; LUNGS ; and FOOD. 



(Carpenter, Principle! of Phyrioloyy, General and Comparative; 

 Carpenter, Manual of Human Phynohgy ; Draper, On the Porca 

 vhick Produce the Organitation of Planti ; Todd and Bowman, 

 Pkyiioloyical Anatomy; Owen, Lecturet on Comparative Anatomy; 

 Lehmann, Physiological Chemittry.) 



HEART'S-EASE. [VIOLA.] 



HEARTWOOD. [ALBURNUM.] 



HEAT, ANIMAL. The conversion of the food of man and the 

 higher animals into nutriment for the body is attended with changes 

 which produce an evolution of heat, which constantly maintains the 

 temperature of an animal at a point above or below, according to 

 circumstances, the temperature of the medium in which it exists. 

 The degree of heat possessed by animals not gifted with the power of 

 locomotion is very small above that of surrounding media, and in 

 this respect resembles the heat given off by plants. [HEAT, VEOE- 

 TAKi.F..] In proportion as animals possess the power of locomotion 

 they evolve heat from their bodies. This arises from the fact that 

 where the muscular system is most exercised there is greatest 

 demand made upon the nutritionary processes going on in the 

 system. We should therefore expect to find that the quantity of 

 heat developed in the invertebrate animals was leas than that in the 

 vertebrate class. Infusoria are for a time capable of resisting cold ; 

 for when the water in which they are contained is frozen, the 

 animalcule is observed to live for a time in a little uncongealed space 

 which the caloric from its body prevents freezing. John Hunter 

 found that various forms of Annelida, as leeches and worms, and 

 several of the Mollutca, exhibit temperatures higher than the sur- 

 rounding media. As might have been anticipated from their activity, 

 the Insects of all the invertebrate animals exhibit the highest 

 temperature. They have been lately the subject of experiment by 

 Mr. Newport. He found that they possessed a temperature above 

 that of the medium in which they lived, varying from 2 to 9 degrees. 

 With respect to the temperature of the different tribes, Mr. Newport 

 observes, " Our previous observations lead us to anticipate the fact, 

 that the volant insects, in their perfect state, have the highest 

 temperature, while, on pursuing the inquiry, it is found that those 

 species which have the lowest temperature are located on the earth. 

 Among the volant insects, those hymenopterous and lepidopterous 

 Hpcric have the highest temperature which pass nearly the whole 

 >t tln-ir active condition on the wing in the open atmosphere, either 

 busily engaged in the face of day despoiling the blossoms of their 

 Iniin.'d treasure!), or flitting wantonly from flower to flower, and 

 breathing the largest amount of atmospheric influence. Of these the 

 hive-bee, with its long train of near and distant affinities, and the 

 elegant and sportive butterflies, have the highest. Next to these are 

 probably their predatory enemies the hornets and wasps, and others 

 of the Mme order ; and lastly, a tribe of insects which have always 

 attracted attention, and in general are located on the ground, but 

 ometirnen enjoy the volant condition the ants, the temperature of 

 whose dwelling has been found to be considerably above that of the 

 atmosphere. Next below the diurnal insects are the crepuscular, the 

 highest of which are the sphinges and moths; and almost equal with 



NAT HIST. DIV. VOL. III. 



them are the Melolontha." In Insects which live in societies the 

 temperature is still greater. Mr. Newport found that a bees'-nest in 

 a chalk bsttik had a temperature 14 to 16 degrees above that of 

 the atmosphere, and 17 to 19 degrees above that of the bank. 



Amongst the vertebrate animals, Fishes and Reptiles have the lowest 

 temperature. Dr. Davy, John Hunter, and others, have found that 

 fishes have a temperature of from 07 to 27 degrees above the sur- 

 rounding medium. 



In man the temperature of the accessible parts of the body, as the 

 mouth, axilla, &c. is usually between 977 and 98'6. The human 

 blood is said to have a temperature in health varying from 100'6 

 to 10175 ; in disease it rises from 106 to 109. In healthy persona 

 the temperature is said to attain its maximum during the day, and 

 to fall from I'l to 27 degrees during sleep. Dr. Davy found that the 

 temperature of the interior of the body is 27 to 3'6 degrees higher in 

 tropical than in temperate climates. Most of the Mammalia have a 

 higher temperature than man, and Birds develop a greater quantity of 

 heat than any other class of animals. This arises from the 

 nutritionary changes going on in the bird in order to support the 

 enormous muscular power which it is compelled to exert during 

 flight. The following is a table of temperatures, as given by Rudolphi 

 and Tiedemann, for several Birds and Mammalia : 



Birds. 



Great Titmouse 

 Swallow .... 

 I-'i-iii'iilla, different species 

 Anas, different species . 

 Common Hen . . 

 Palm, different species 

 Pigeon ..... 

 Raven .... 

 Vulture .... 



Common Cock 



White Game .... 

 Gull ..... 



Mammalia. 



Bat ( Vespertilio pipiitrellua) . 

 Squirrel .... 

 Sheep ..... 

 Ox ..... 

 Rabbit ..... 

 Ape ..... 

 Cat ..... 

 Bat ( Vetperlilio noclula) 

 Dog ..... 

 Guinea Pig . 



Hare ..... 

 Elephant .... 

 Horae ...... 



Degrees. 

 111-25 

 111-25 



111-25 to 107 

 111 to 106 

 109-94 to 102-99 

 10974 to 104-5 

 109-58 to KMi-7 

 109-23 to 105-99 

 107.49 



10378 to 102-99 

 102 

 100 



Degrees. 

 106 to 105 

 105 



104 to 100-4 

 104 to 99 

 104 to 99-46 

 103-86 



103-6 to 98 6 

 102 



101-3 to 99 3 

 100-4 to 96-37 

 100 

 99-25 

 98-24 to 97 



There is now no question that the cause of animal heat is the 

 chemical changes which are going on in the nutrient fluid of the 

 body. During the act of respiration a large quantity of oxygen gas 

 is taken into the lungs, which is absorbed by the blood. In this fluid 

 it meets the various compounds of carbon which have been taken in 

 with the food; and the consequence is a union of the oxygen witli 

 the carbon, and the formation of carbonic acid gas, which gas is 

 given out when the blood again reaches the lungs, during expiration. 

 [KooD; RESPIRATION.] When carbon and oxygen unite out of the 

 body, heat is the result, and the same thing occurs when they unite 

 in the body ; and it is through the medium of this change that tho 

 bodies of animals are raised to a given temperature by the circulation 

 of the blood through the system. It has been calculated that there 

 is more oxygen absorbed than is given out of the system in the form 

 of carbonic acid gas : it is probable that this enters into combination 

 with hydrogen, forming water and other compounds of hydrogen, 

 nitrogen, and carbon, and thus contributes to the raising of the 

 animal beat. 



This theory of animal heat explains many well-known phenomena ; 

 as for instance, the slight independent warmth of the footus, and of 

 those young animals which are born in an imperfectly developed 

 condition. The low temperature of persons with morbus cteruleus, 

 where the blood is only imperfectly oxygenated, and the cold expe- 

 rienced by aged and debilitated persons iu whom a small quantity of 

 blood circulates slowly ; as also the increased temperature observed in 

 persons labouring under attacks of inflammatory disease where thu 

 blood circulates rapidly, are also confirmatory facts. The phenomena 

 also exhibited by the hyberuation of animals are explained by thin 

 theory. During the period of hybernation, when the blood is circu- 

 lating only slowly and respiration is almost suspended, and the 

 oxygenation of the blood is feebly performed, the temperature of the 

 animal is low. The observations of Pallas and others show that 

 hybernation is prevented by a temperature of from 50 to 80", whil-t 

 it is induced in those animals which exhibit it even in summer by tho 

 application of artificial cold. 



I 



