GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 131 



was the result of inability to relax. Relaxation as well as contraction is to be 

 regarded as an active process, and in fatigue the power both to contract and 

 relax is lessened. 



The prolonged contraction of the fatigued muscle is chiefly caused by the 

 injurious effects of the waste products produced within it as a result of the 

 chemical changes accompanying its activity. One of these waste products, 

 sarcolactic acid, is known to have the effect to prolong muscular contractions, 1 

 and it is not unlikely that others may exert a similar influence. 



In case the muscle be excited frequently and for a considerable time, 

 the contraction effect and the decreased power of relaxation due to fatigue, 

 toward the end of the experiment, may both be present at the same time, and 

 both act to prolong the curve of contraction. This was probably the case in 

 the experiments the records of which are given in Figures 47 and 48, and 

 many of the figures employed to illustrate the development of tetanus. 



An example of this is to be seen in the effect of certain chemical sub- 

 stances on the muscle. For example, the withdrawal of water by drying, by 

 the application of glycerin, or by a strong solution of sodium chloride, may, 

 by rapidly altering the constitution of the protoplasm, cause an increase of 

 excitability which may pass over to a state of excitation, which will be man- 

 ifested by irregular but more or less continuous contractions. Such contrac- 

 tions are of the type of an incomplete tetanus. 



Effect of Constant Battery Current. — Attention has already been called to 

 the fact that under certain circumstances a form of continuous contraction 

 may be excited by a continuous constant electric current. If the current be 

 very strong, the short closing contraction may be followed by a more or less 

 continuous contraction — the closing (or Wundt's) tetanus ; and the short open- 

 ing contraction may be followed by another continuous contraction, which 

 only gradually passes off— the opening (or Ritter's) tetanus. This form of 

 contraction is quite readily excited in normal human muscles by both direct 

 and indirect excitation. The term " galvanotonus " is sometimes employed 

 for the continuous contraction of human muscles excited by the continuous 

 flow of a constant current. 



Although a continuous contraction caused by the constant current is 

 spoken of as tetanus, it is a matter of doubt whether it is a true tetanic con- 

 dition, for the term tetanus is limited to a form of contraction which, though 

 apparently continuous, is really an interrupted process, and results from 

 many frequently repeated stimuli. Von Frey 3 expresses the view that the 

 continuous contraction which follows the closing of the continuous constant 

 current is a form of tetanus. It is certainly true that the closing tetanus 

 often shows irregular oscillations, suggestive of a more or less intermittent 

 excitation which might be explained on the supposition that the flow of the 

 current produces electrolytic decompositions within the tissue, and that the 

 liberated ions exciting the protoplasm of the different fibres irregularly lead 



1 Lee: American Journal of Physiology, 1899, vol. ii. p. 11 



2 Arrhirjiir . I iiatninif iiihI I'ln/siolotjie, 1885, S. 55. 



