i GENERAL PHYSIOLOGY OF MUSCLE 59 



This exhaustion depends on the absence of a proper supply of 

 oxygen and nutrient material to repair the waste of substance in 

 the active muscle and nerve-centres, and to the accumulation of 

 metabolites which paralyse the tissue owing to the arrest of the 

 blood and lymph circulation. Ranke, in fact, showed that, on 

 merely circulating a saline solution that contained no nutrient 

 restorative matters through fatigued frog-muscle, the signs of 

 fatigue disappeared. If, on the other hand, an aqueous extract of 

 the fatigued muscle of one frog were circulated through the fresh 

 muscle of another, fatigue phenomena at once set in. 



Mosso continued these researches on warm-blooded animals, 

 and showed that transfusion of the blood of a fatigued into the 

 vessels of a normal dog induced symptoms of respiratory, cardiac, 

 and general fatigue in the latter. Clearly, therefore, the waste 

 products of muscular activity act as toxic substances, and cause 

 muscular fatigue and exhaustion. 



The inexhaustibility of the flexor muscles of the middle finger 

 or the abductors of the index finger, under the experimental 

 conditions adopted by Treves, Schenck, and others, is not sur- 

 prising, and seems indirectly to confirm Ranke's theory of the 

 causes of muscular fatigue and exhaustion. 



X. Only a small part of the potential energy liberated in 

 muscular contraction is used up in the form of external work ; 

 the other, considerably larger, part is converted into internal work, 

 which is accompanied by the development of heat. 



It is a common observation that after vigorous effort or 

 repeated contractions of the muscles the temperature of the body 

 rises ; every one knows that muscular activity is the best way of 

 warming oneself in cold weather. In walking and running the 

 rectal temperature may rise some tenths of a degree. In tetanus 

 the fever may reach a high degree (45 '3 C., according to Wunder- 

 lich). The same is seen in strychnine poisoning (44 C., Vulpian). 



On the other hand it has long been known that in a state of 

 absolute muscular rest, as in sleep, the internal temperature falls 

 about half a degree centigrade, and rises again rapidly on waking. 

 The mere immobilisation of an animal, or its curarisation, cools it 

 to 30 '7 C. (Richet), and a subsequent injection of strychnine is 

 no longer able to evoke spasms or to raise the temperature, which 

 must therefore depend on the tetanising action of the strychnine. 



Since the muscles represent about 40 per cent of the total body 

 weight in vertebrates, and after removal of the skeleton (which 

 can only develop a negligible amount of heat) certainly represent 

 more than 50 per cent, and since katabolism is more active in 

 muscle than in any other tissue, we are justified in assuming 

 that the muscles have a preponderating influence on the heat pro- 

 duction of the body, in comparison with that of all other tissues. 



We shall elsewhere discuss thermogenesis and the thermal 



