INFLUENCE OF NERVOUS SYSTEM ON HEAT PRODUCTION 439 



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 path 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, and 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 must indicate not only too rapid metabolism 

 of the body, but also insufficient time for the tissues to build themselves up. 

 In fever, then, there may be supposed to be some interference with the ordinary 

 reflex channel by which the skin is able to communicate to the nervous sys- 

 tem the necessity of an increased or diminished production of heat in the 

 muscles and other tissues. In consequence of this, and in spite of the con- 

 dition of increased heat of the body, both at the surface and in the deeper 

 tissues, the production of heat goes on at an abnormal rate. It is not certain 

 whether the pathological condition is one which stimulates the thermogenic 

 center by means of which the metabolism of the tissues is increased, or whether 

 the normal reflexes which ordinarily inhibit the activity of the center v/hen 

 the temperature rises fail to bring about their usual reaction. The first is 

 the probable explanation of the high fevers of certain toxemias, 



