442 



THE FUNCTIONS OF CROSS- STRIATED MUSCLES 



short. Consequently in these muscles the above-mentioned incomplete tetani are 

 entirely wanting. 



[According to F. S. Lee this difference in the mode of fatigue between the 

 excised muscles of cold-blooded and of warm-blooded animals is due to a real 

 physiological difference and not, as had been supposed by Schenck and Lohmann, 

 to a mere difference of temperature. Lee finds that the muscles of the former 

 exhibit the same characteristic slowing of the contraction process (cf. Fig. 178) 

 both at low and at high temperatures (though at the high temperature to some- 

 what less extent than at the low) ; whereas the muscles of the latter do not 

 exhibit this phenomenon at either high or low temperatures. " The poikilother- 

 mal condition (cf. page 46) is more primitive than the homoiothermal, and it 

 would seem that the constant influence of a uniform temperature acting for ages 



on the skeletal muscles of 

 warm-blooded animals has im- 

 pressed on them certain pro- 

 nounced peculiarities." Pos- 

 sibly the part which these 

 muscles themselves play in 

 the production of heat is in 

 some way associated with 

 this physiological difference. 

 ED.] 



With regard to the fa- 

 tigue of nerves we must dis- 

 tinguish very clearly between 

 the local fatigue which takes 

 place in artificial stimula- 

 tion at the point where the 

 stimulus is applied, and 

 which in part at least is due 

 to the injurious effects of 

 the stimulating agent, and 



201 ^Sm^H^^^^^^^^H^BHM^HHi^MHiS the fatigue which is pro- 

 duced possibly by the trans- 

 mission of stimuli. Since 

 only the latter determines 

 the normal behavior of nerve, 

 we shall discuss it alone. 



In order to observe the 

 fatigue of nerve, it is neces- 

 sary to so arrange the ex- 

 periment that its muscle is 



not stimulated. Bernstein fulfilled these requirements by stimulating the sciatic 

 nerve of the frog a long distance from the muscle, at the same time conducting 

 through the nerve between this point of stimulus and the muscle a strong con- 

 stant current. The resistance at the anode of the constant current prevented 

 the stimulus applied farther up from reaching the muscle. In this way Bern- 

 stein found that the nerve was much less capable of fatigue than the muscle. 

 By the same method Wedensky was able to stimulate a motor nerve of the frog 

 for six hours without exhausting it. 



This same resistance of nerves to fatigue has been demonstrated also by 

 Langendorff, Bowditch and others, on warm-blooded animals. If curare, which 

 throws out of action the end plates of the motor nerves, be administered to an 



FIG. 178. Isotonic contractions of a frog's gastrocne- 

 mius, after F. S. Lee, showing changes due to fatigue. 

 Only every fiftieth contraction is recorded. 



