

ADVANCED EXPERIMENTAL PHYSIOLOGY 107 



Bayliss introduced the use of a solution of gum. We further see 

 that, when isotonic solutions of electrolytes are used, the tissues are 

 by no means indifferent to the ions in solution. A really " normal " 

 saline solution would, therefore, be one which contained the same 

 salts in the same proportion as the animal's own blood-plasma. 

 Ringer's l fluid is an attempt to make such a solution for the 

 frog. 



In all the above experiments it has been found that skeletal muscle 

 responds to the abnormal constant stimulus by an activity which 

 is not constant, but intermittent or rhythmical. This raises the 

 question whether the rhythmical contraction of the heart may not be 

 the normal response of that particular kind of muscle to the constant 

 chemical stimulus of the blood-plasma, and the same might be also 

 partly true of the rhythmical activity of the respiratory and vaso- 

 motor centres. 



CHAPTER VIII 



FATIGUE OF A VOLUNTARY MOVEMENT AND OF A MUSCLE- 

 NERVE PREPARATION WITH ITS CIRCULATION INTACT 



When a voluntary movement is repeated sufficiently often fatigue 

 is produced. The seat of this fatigue has to be investigated ; it 

 might be in some part of a neurone in the central nervous system, or 

 in some part of the peripheral nerve and muscle : in other words, 

 the fatigue might be primarily central or peripheral. As the result 

 of certain ergographic experiments it has been answered that this 

 fatigue is of central origin. The experiments consisted in lifting a 

 heavy weight suspended over a pulley by flexing a finger and 

 registering the height of each successive lift. When the movement 

 had been repeated until the muscle was no longer able to lift the 

 weight at all, it was found that electrical stimulation of either the 

 nerve supplying the muscle or of the muscle itself caused the weight 

 to be again lifted, but to a less height than before. When the 

 electrical stimulation had in turn fatigued the movement it was 

 found that a voluntary contraction of the muscle was again able to 

 lift the weight, owing, it was supposed, to the resting of the cells 

 in the central nervous system. From these experiments it was 

 argued that the fatigue of a voluntary movement is purely central. 



The methods used in the above experiments are open to grave 

 objections, and it is necessary to touch upon some of these in order to 

 avoid them. The use of a heavy weight is open to the objection that 

 the muscle, when no longer able to lift that weight, is still capable of 

 contracting, and could well lift a lighter weight ; therefore, it is better 

 to make the muscle bend or pull on a spring, which will enable the 

 feeblest as well as the strongest pull exerted by the muscle to be 



1 A modified Ringer's solution contains NaCl -7 per cent., CaCl 2 -0026 per 

 cent., and KC1 -035 per cent. 



