2;] 4 FKVKIl. 



(lucliuii of lioat. The conclusion thus rraclicd takrn in conjunction with the farts 

 that licat still continues to be produced in starvation, and that various functional 

 netions, as uiuscular movement and secretion in animals, and Ho\vi'rin<^ in plants, 

 have been found by various experimenters to be causes of local heal dexelopment, 

 indicates that there are in the animal economy two distinct general sources of 

 heat: first, the destruction, which proljably occurs in the blood, of the excess of 

 crude food material ; second, nutritivi' changes in tissue, includtn<; all changes in 

 the blood itself at the expense of its permanent constituents. It has not been 

 proven, but it is most \irobable, that the heat centre, investigated in the previous 

 chapter, affects solely the latter source of animal heat. 



The effect of the ingestion of food upon heat production is so great and imnif»- 

 diate that, if we desire to discover whether there is a diurnal cycle of alteration in 

 tlu' heat production, we must look at the rcconls of those days when no food was 

 taken, I. c, when tliere was the greatest freedom fnun known disturbing causes. 

 Hanging side by side the records of the four experiments at command for present 

 purposes, and inverting the time as necessary to make the records coincide as nearly 

 as possilde, we obtain the following table. Kach experiment consists of a con- 

 nected twenty-four hours, altliough the periods of time did not always actually 

 follow one another as arranged in the table. 



KxrF.BiME.NT 112. Experiment 114. 



X,v« Hr.AT ^ Hfat 



"" rBi'iii-iTiox. imi. Proiiiitios. 



5:11 P.M. to 10:11 P.M. 58.0187 8:15 p. ii. to 11:1.'. r. m. 53.4404 



11:3 P.M. to 4:3 a.m. C9.H7.'>G r.':47 a. m. to 6:47 a.m. .52 5167 



5 A.M. to 10 A.M. 63.86 9:20 a. M. to 2:20 p.m. 61.7988 



12:13 p.m. to 4:13 p.m. 84 159 3:37 p. m. to 7:37 p.m. 75.42'.I9 



When these experiments were performed the use to which they are at present 

 being put was not thought of. The ])eriods of calorimetrical observation do not 

 therefore correspond closely. Nevertheless the general drift is sufficiently similar 

 for comparison. If we tabulate the periods of maximum and niinimuin production 

 tlii-y will stand as follows: — 



Espmii>c«T. .Mi.vi>iix Pcitinn. Mimmi M Pkrioo. 



110 1:30 P. M. to 3:;J0 I'. M. 12:10 a. M. to 5:10 a.m. 



113 12:13 P. M. to 4:l:j P. M. 5:11 p. >l. to 1 1 :1 1 P. >l. 



in 3:37 P. M. to 7:37 P M. 8:15 p. m. to 11:4,". p m. 



On looking over this tabulated statement it will be seen that whilst there is some 

 correspondence there is also a good deal of divergence. The time of maximum 

 heat productioji in all is earlier or later in the afternoon; in two the time of mini- 

 mum heat production is in the evening. This indicates that there is usually a 

 tendency in normal dogs to an increase of heat ])roduction in the al'ternoon, and a 

 diminution of it in the evening. The experiments are, however, not altogether 

 concordant, and are tf)o few to setth' the (|Uestion: but it is evident that if n ten- 

 dinry ta a rhythmical production of animal heat does exist, such tendency must 

 be entirely subservient to the arciclents of feeding, exercise, etc., and that at least 

 in the dog any diurnal cych- of bodily teniperatttre which may exist must be de- 



