78 PHYSIOLOGY CHAP. 



not stimulate organic combustion when it acts directly on the 

 internal organs, on which thermogenesis mainly depends. The 

 cooling of the inside of the body througli the lungs or the stomach, 

 for instance, when one breathes through a very cold metal tube, 

 surrounded by ice, or drinks iced water, or when the stomach of a 

 dog is flushed with iced water through a gastric fistula, does not 

 cause an increase but rather a marked diminution in the gaseous 

 respiratory exchange. Even when cold acts on the periphery of 

 the body, it produces not an increase but a decrease in the 

 respiratory processes of the internal tissues, if the cooling of the 

 skin goes beyond the limits already given, and lowers the internal 

 temperature of the animal (Ludwig and Sanders - Ern). It is 

 this process which renders death from freezing possible in the very 

 low temperatures of the polar regions or lofty mountain peaks. 

 When warm-blooded animals are exposed under such conditions, 

 they respond like cold-blooded animals, which possess no means 

 of regulating their production of heat. Such a regulation only 

 protects from cold within certain limits, which vary in different 

 warm-blooded animals. In all cases it is effective only when the 

 cold acting on the periphery of the body does not succeed in 

 lowering the internal temperature of the animal below the 

 normal. 



It is evident that the thermic regulation which takes place in 

 such cases works through the reflex action of the nervous system. 

 The sensory organs of the skin, stimulated by the action of the 

 low temperature, cause through the intervention of the centres 

 an exaggeration of the internal respiration of the tissues, almost 

 in proportion to the sensation of cold. Since the muscles, by 

 reason of their preponderance and the intensity of their respira- 

 tion, are the chief seats of the production of heat, we may hold 

 with Pflliger that reflex action of the centres in the regulation of 

 temperature involves especially the motor nerves of the muscular 

 system. 



While, therefore, the reflexes, acting on the blood - vessels, 

 regulate the loss of heat, the reflexes acting at the same time on 

 the muscles regulate the production. We know that the nerve- 

 centres normally exercise a tonic reflex effect on the muscular 

 system. 



This tonic action cannot be dissociated from a continuous 

 stimulation of the ' respiratory process, which takes place in the 

 muscles independently of their contraction. C. Bernard proved 

 by analysis of the gases of the blood that after the severance of 

 the motor nerves the respiration of the paralysed muscles becomes 

 less active than that of the normal muscles at rest, but connected 

 with the cerebro-spinal centres. The clinical fact that in cases of 

 herniplegia the paralysed limbs become after a certain time colder 

 than the limbs on the healthy side, independently of any active 



