THE ENERGY OF THE BODY. 505 



some more than others, at such a spendthrift rate that their capital is soon 

 exhausted. We have seen ( 314) that too warm blood produces dyspnoea 

 and soon exhausts the metabolic capital of the respiratory centre. Too 

 warm blood similarly hurries on the beats of the heart ; an explosion of the 

 contractile substance is each time prematurely brought on before a sufficient 

 quantity of explosive substance is accumulated, each stroke becomes more 

 .and more feeble as the rate is quickened, the beats become irregular and 

 finally cease. Either of these two events alone and certainly both together 

 are enough to bring the working of the bodily mechanism to an end ; but 

 other tissues beside the heart and the respiratory centre are suffering in the 

 same way, notably the rest of the central nervous system. This, too, is 

 being hurried on unduly in its inner changes, so that not only consciousness 

 is lost and other objective manifestations of nervous action go wrong or fail, 

 but the regulative grasp of the central nervous system on the tissues of the 

 body at large is loosened, and tumult takes the place of order. Whether 

 this or that sign of disorder comes to the front, whether, for instance, 

 convulsions take place, would appear to depend upon the exact turn 

 taken by the abnormal events. In heat-stroke, more commonly known as 

 sun-stroke, the essential condition of which seems to be a rapid rise of the 

 temperature of the body, owing to a sudden failure of the thermotaxic 

 mechanism, the symptoms vary. Sometimes the heart suddenly gives 

 way, at other times the respiratory centre seems to be more directly 

 affected ; sometimes convulsions make their appearance, but more com- 

 monly death takes place through a comatose condition of the brain, an 

 initial phase of excitement of the central nervous system being not uufre- 

 quently witnessed. 



Mammalian muscle, it will be remembered ( 82), becomes rigid at 

 about 50 ; but death probably always occurs before that higher tempera- 

 ture is reached by the blood, so that a sudden rigor mortis from heat 

 (rigor caloris) cannot be regarded as a factor in death from exposure to 

 too great heat. 



453. Effects of great cold. The effects of a too great lowering of the 

 temperature of the body, which is, generally, the result of too great ex- 

 ternal cold, and rarely, if ever, arises from internal causes lowering the 

 metabolism and thus the production of heat, are, in their origin, the reverse 

 of those of a too high temperature. The metabolism of the tissues is low- 

 ered ; and not only are the katabolic changes, which lead to the setting free 

 of energy thus affected, but the anabolic changes also share in the depres- 

 sion. Thus " living substance " falls to pieces less readily, but is also made 

 up less readily ; and could this slackening of metabolism be carried on in 

 the several tissues at a rate proportionate to the rate at which each tissue 

 lives, life might thus be brought to a peaceful end by gradual arrest of the 

 life of each part of the whole body. And, indeed, in some cases, where the 

 lowering of the temperature takes place gradually, something like this does 

 occur even in warm-blooded animals. The diminished metabolism tells first 

 and chiefly on the central nervous system, especially on the brain, and more 

 particularly on those parts of that organ which are concerned in con- 

 sciousness. The intrinsic lowering of the cerebral metabolism is further 

 assisted by a slowing of the heart-beat and of the breathing ; drowsiness is 

 succeeded by a condition very like to, if not identical with, that known 

 as sleep, which we shall study later on, but by a sleep which insensibly 

 passes into the sleep of death. In sonie cases, however, especially those 

 in which the lowering of the temperature is sudden and rapid, disorders of 

 the nervous system intervene and convulsions like those of asphyxia are 

 produced'. 



