2 ANATOMY OF VERTEBRATES. 



blood, changed by the resph'atory action, is conveyed to another 

 distinct auricle and propelled by a second distinct ventricle over 

 the entire system. 



Thus a four-chambered heart and spongy lungs are the chief 

 anatomical characteristics by which the ^ warm-blooded ' are dis- 

 tino-uished from the ^ cold-blooded ' Vertebrates, although respira- 

 tion and circulation are subsidiary or auxiliary, not immediate, 

 thermoo-enous functions. 



Whatever tends to obstruct the flow of blood to a part of the 

 body, as ligature of an artery, e. g., lowers in a certain degree the 

 heat of that part ; and whatever augments such flow of blood, as, 

 exercise, e. g., or increases the quantity of blood in a part, as 

 where the capillaries dilate through paralysis of the vaso-motory 

 filaments from a ganglion of the sympathetic nerve, raises the heat 

 of such part; temporarily, at least, in the latter case.^ 



In all HcEmatotlierma the mass of nervous matter constituting 

 the cerebral portions of the prosencephalon is relatively larger 

 both to the rest of the brain and to the bulk of the body than in 

 Hcpmatocrya, although the degrees of this predominance in the 

 warm-l)looded series relate to other functions than the evolution 

 of heat. 



Concomitantly with the advance of the circulating and respira- 

 tory organs in HcEmatotlierma is that of the blood itself, in quantity, 

 in the proportion of organic {proteine) principles to the water in it, 

 and in depth of colour due to the more abundant blood-discs. 

 The voluntary muscular fibre shows, in most Hcematotherma, by 

 its deeper colour than in Hcematocrya, the influence of this more 

 abundant, richer, and redder blood ; and the longer duration and 

 greater energy of the contractions have relation to the ha^mato- 

 thermal conditions of the nervous, respiratory, and circulating 

 systems. 



In every muscular contraction some molecules of the fibre 

 may be said to be burnt, and heat is evolved. Needles of a deli- 

 cate thermo-electrical apparatus, thrust into a living muscle, indi- 

 cate a rise of temperature at each act of contraction. ^ The heat- 

 producing results of the sum of such actions is a matter of common 

 experience, and a loss of animal heat results from the cessation of 

 such actions. So, Hunter writes : ^ When a man is asleep he is 

 colder than when he is awake ; and I find, in general, that the 

 difference is about one degree and a half (of Fahr.)^ 



' V. p. 377. 



- As in the ' biceps flexor ciibiti ' of the man so experimcntctl on, in i-. p. 402. 



^ xciv. p. U-4. Sec also ir. 



