468 ANIMAL HEAT 



a warm-blooded animal when exposed to cold, and the corresponding increase 

 in the output of carbon dioxide, indicating that there is an increase of the 

 metabolism and so an increased production of heat under such circumstances, 

 and not a mere diminution of the amount of heat lost by the skin, etc. A 

 cold-blooded animal reacts very differently to exposure to cold; instead of 

 increasing the metabolism as in the case of the warm-blooded animal, cold 

 diminishes the metabolism of its tissues. It is clear, therefore, that in warm- 

 blooded animals there is some apparatus not possessed by cold-blooded ani- 

 mals, which counteracts the effects of cold. In warm-blooded animals poi- 

 soned by curara, or in which section of the medulla has been done, it has been 

 found that this regulating apparatus is no longer in action, and under such 

 circumstances no difference appears to exist between such animals and those 

 which are naturally cold-blooded. Warmth increases their temperature, 

 and cold lowers it, and with this there is, of course, evidence of diminished 

 metabolism. 



The explanation of these experiments is that in such animals the connec- 

 tion between the skin and the muscles through the nervous chain, such as 

 a thermotaxic nervous apparatus might be supposed to afford, is broken 

 either at the termination of the nerves in the muscles (curara) or at the sec- 

 tioned point of the bulb. 



The position of these hypothetical centers is a matter of some difference 

 of opinion. It has been demonstrated that stimulation of certain parts of 

 the brain may, among other symptoms, produce increased metabolism of the 

 tissues with increased output of carbon dioxide and a raised temperature: 

 the parts of which this may be asserted are parts of the corpus striatum and 

 of the optic thalamus. The general thermogenic centers are probably closely 

 associated with the motor centers of the cord and brain stem. The thermo- 

 regulative centers are the nuclei in the corpus striatum and optic thalamus. 

 Assuming a constant or tonic activity of the thermogenic regulative centers, 

 it is easy to understand the fall of temperature on their destruction or on the 

 destruction of the nerve paths to the active tissues. 



Experimental observations, such as have been made upon animals, 

 receive confirmation from the observations on patients who suffer from fever 

 or pyrexia; in them the temperature of the body may be raised several de- 

 grees, as we have already pointed out. This increase of temperature 

 might, of course, be due to diminished loss of heat from the skin, but this, 

 although a factor, is not the only cause. The amount of oxygen taken in 

 and the amount of carbon dioxide given out are both increased. With 

 this there must be increased metabolism of the tissues, and particularly of 

 the muscular tissues, since at the same time the amount of urea in the urine 

 is increased. Every one is familiar with the rapid wasting which is such a 

 characteristic of high fever; it indicates not only too rapid metabolism of 

 the body, but also insufficient time for the tissues to again build themselves 



