346 Dr. K. Sassa. Effects of Constant Galvanic Currents upon 



any external stimulus, a weak tetanus, which is either augmented or depressed 

 by the onset of catelectrotonus or anelectrotonus. It may be therefore 

 supposed that in a fresh mammalian nerve, even immediately after isolation, 

 subliminal stimuli due to injury are present, and when the impairment of the 

 nerve is advanced, the muscle is already in a state of weak tetanus. 



The closure and opening tetanus seen in the mammal may be explained in 

 the same way as in the frog, if we assume that these subliminal stimuli due 

 to injury and exposure become effective from the positive modification in 

 excitability at the catelectrotonic tract of the nerve during the closure of the 

 current, and at the previously anelectrotonic tract on opening the current. 



The question arises here as to whether these pre-existing stimuli are due 

 to an injury current or to other intrinsic causes connected with the dying 

 process of an isolated tract of the nerve. To decide this, the sciatic nerve 

 was divided twenty-four or more hours before the experiment, since the 

 injury current diminishes greatly in that time. The results obtained in such 

 preparations were identical with those already described. The injury current 

 does not appear, therefore, to play an important role in this respect. When 

 the animal is left alive more than forty-eight hours after aseptic division of 

 the sciatic nerve, the threshold value of the nerve rises, and continuous 

 excitation is no longer obtained during the passage of strong currents in 

 either direction. Even in the third stage of the excitation formula, no appre- 

 ciable tetanus takes place during the flow of descending current through the 

 nerve. The nerve loses entirely its mechanical and electrical excitability if 

 the animal is allowed to survive three days after the nerve section. This 

 reaction of degeneration does not directly concern us here. 



II. Experiments on the Flexor Reflex Preparation. 



These results are on the whole similar to those obtained in the nerve- 

 muscle preparation. The threshold value for the spinal preparation was often 

 found to be nearly as low as that of the nerve-muscle preparation. It was, 

 however, much higher in the decerebrate (sometimes more than ten times 

 higher) than in the nerve-muscle preparation (Sherrington (14) and others). 



Pfliiger (7) himself showed that the law which he formulated for the motor 

 nerves held for the afferent nerves of the frog. In the mamniaLiau reflex 

 preparation, the second and third stages are more easily demonstrated than 

 the first. The first stage can usually be verified if the threshold value is low. 

 When it is high, as in the decerebrate preparation, the contraction at break 

 of the ascending current often makes its appearance at a lower value of the 

 current stimulus than does the contraction at make, while the reverse is true 

 of descending currents. 



