4OO VARIATIONS IN HEAT-PRODUCTION. 



ESTIMATION OF HEAT-INCOME ACCORDING TO FRANKLAND'S 



METHOD. 



Frankland in 1866 burned food directly in the calorimeter (Fig. 133) and 

 obtained the following results : 



i gram of proteids yielded 4998 heat-units 1 These figures may be 



grape-sugar yielded 3 2 77 r compared with Rub- 

 beef-fat yielded 9069 J ner's results, p. 379. 



The proteids are decomposed only to the stage of urea ; therefore the heat yielded 

 by the combustion of the latter is to be deducted from 4998, thus leaving 4263 

 heat -units for i gram of proteids. If the number of grams of the individual foods 

 taken by man has been determined by weight the number of heat-units taken up 

 can be readily estimated. 



When the amount of food is sufficient the production of heat, under otherwise 

 like conditions, is always the same. If the amount of food is insufficient, the 

 amount of heat produced is but little diminished, as the body must then consume 

 some of its own tissues. This is naturally the case in the state of hunger especially. 

 The character of the food, providing it is sufficient in other respects, is of subor- 

 dinate importance. 



VARIATIONS IN HEAT-PRODUCTION. 



According to v. Helmholtz the average heat-production in a healthy adult, 

 weighing 82 kilos, in twenty-four hours is 2,732,000 calories. 



Influence of the Superficies of the Body. Rubner found that heat- 

 production is dependent not upon the weight of the body, but upon 

 its size and the related superficies. Small, and also young, animals 

 have a relatively larger superficies than larger, and also older, animals. 

 As, however, the dissipation of heat takes place principally from the 

 external surface, accordingly greater heat-production will have to take 

 place in animals with a greater superficies heat-dissipating surface. 

 Thus a relatively greater consumption of oxygen was accordingly ob- 

 served in smaller animals. Rubner's investigations have shown that for 

 dogs of various sizes the heat-production for each square meter of body- 

 surface uniformly equaled 1,143,000 calories. If the body- weight was 

 compared with the body-surface in different animals, he found that for 

 every kilogram of weight there was in the rat 1650, in the rabbit 946, 

 in man 287 square centimeters of surface. 



According to J. Rosenthal the production of heat is to be estimated in the 

 following manner: If n represents the amount of heat produced in an animal 

 in one hour, g the body- weight, and A a factor that remains nearly constant in the 

 same species and under like nutritive conditions (for the body of the child, 11.97 > 

 for that of the adult, 12.31; for that of the dog' 49; for that of the rabbit, 33), 



then n = A^/g 2 . 



Age and Sex. In the earliest period of life, as well as in old age, the production 

 of heat is less than at mature age. It is likewise so in women as compared 

 with men. 



Daily Variation. The production of heat exhibits a course similar to that 

 of the bodily temperature at different hours of the day. 



Bodily Functions. During waking, with physical and mental exertion, as 

 well as during digestion (on account of the greater glandular activity) , the pro- 

 duction of heat is greater than under the opposite conditions. 



RELATION OF HEAT-PRODUCTION TO THE WORK PERFORMED 



BY THE BODY. 



The potential energy supplied to the body can be transformed by the 

 latter into heat and into kinetic energy. In the resting body almost the 



