452 NUTRITION ANIMAL HEAT AND FORCE. 



the anterior portion of the upper surface of the brain, near the median line 

 (Eulenberg and Landois). The conductors connected with these centres 

 decussate and pass through the medulla oblongata and the spinal cord. The 

 question arises as to whether the effects of puncture or stimulation of these 

 parts be exciting or inhibitory ; but observations regarding the mechanism 

 of their action have not been sufficiently definite to warrant any positive con- 

 clusions on this point. 



MECHANISM OF THE PRODUCTION OF ANIMAL HEAT. 



The definite ideas of physiologists concerning the mechanism of the pro- 

 duction of heat by animals date from the researches of Lavoisier (1777 to 

 1790). As a general result of these observations, Lavoisier concluded that 

 animal heat was produced by an internal combustion resulting in carbon 

 dioxide and water. Even now there is little to be said beyond this, as regards 

 the general mechanism of animal calorification, although modern investiga- 

 tions have brought to light many important details in the heat-producing 

 processes. 



In man and in the warm-blooded animals generally, the maintenance of 

 the temperature of the organism at a nearly fixed standard is a necessity of 

 life ; and while heat is generated in the organism with an activity that is 

 constantly varying, it is counterbalanced by physiological loss of heat from 

 the cutaneous and respiratory surfaces. Variations in the activity of calori- 

 fication are not to be measured by corresponding changes in the tempera- 

 ture of the body, but are to be estimated by calculating the quantity of heat 

 lost. The ability of the human race to live in all climates is explained 

 by the adaptability of man to different conditions of diet and exercise, and 

 by the power of regulating loss of heat from the surface by appropriate 

 clothing. 



Heat is produced in the general system and not in any particular organ 

 or in the blood as it circulates. The experiments of Matteucci, showing an 

 elevation of temperature in a muscle excited to contraction after it had been 

 removed from the body, and the observations of Becquerel and Breschet, 

 showing increased development of heat by muscular contraction, are sufficient 

 evidence of the production of heat in the muscular system ; and inasmuch 

 as the muscles constitute by far the greatest part of the weight of the body, 

 they are a most important source of animal heat. It has been observed that 

 the blood becomes notably warmer in passing through the abdominal viscera 

 (Bernard). This is particularly marked in the liver, and it shows that the 

 large and highly organized viscera are also important sources of caloric. 



As far as it is possible to determine by experiment, not only is there no 

 particular part or organ in the body endowed with the special office of calori- 

 fication, but every part in which the nutritive forces are in operation pro- 

 duces a certain quantity of heat ; and this is probably true of the blood-cor- 

 puscles and other anatomical elements of this class. The production of heat 

 in the body is general and is one of the necessary consequences of the process 

 of nutrition ; but, with nutrition, it is subject to local variations, as is illus- 



