650 EFFECTS OF GREAT HEAT AND COLD. [Book n. 



condition of which seems to be a rapid rise of the temperature 

 of the body owing to a sudden failure of the thermotaxic mech- 

 anism, 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 ap- 

 pearance, but more commonly death takes place through a 

 comatose condition of the brain, an initial phase of excitement 

 of the central nervous system being not unfrequently witnessed. 



Mammalian muscle, it will be remembered, § 79, becomes 

 rigid at about 50° ; but death • probably always occurs before 

 that higher temperature is reached by the blood, so that a sud- 

 den rigor mortis from heat (rigor caloris) cannot be regarded 

 as a factor in death from exposure to too great heat. 



§ 433. Effects of Great Cold. The effects of a too great 

 lowering of the temperature of body, which is generally the 

 result of too great external cold and rarely if ever arises from 

 internal causes lowering the metabolism and thus the produc- 

 tion of heat, are in their origin the reverse of those of a too 

 high temperature. The metabolism of the tissues is lowered; 

 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 depression. The "living substance" falls to pieces less 

 readily, but is also made up less readily; and could this slack- 

 ening 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 gradu- 

 ally, something like this does occur even in warm-blooded ani- 

 mals. The diminished metabolism tells first and chiefly on the 

 central nervous system, especially on the brain and more particu- 

 larly 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 

 breath, 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 some 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. 





