CHAPTER II. 

 THE GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE. 



VII. ELECTRIC APPARATUS AND UNITS OF MEASUREMENT. 



THE function of muscle tissue is to contract. Muscles contract 

 only in response to stimuli. Stimuli may act upon the muscle tissue 

 direct stimulation; or upon the motor nerve which supplies the 

 muscle indirect stimulation. To study the functions of muscles and 

 nerve tissue one requires to have at command various methods of 

 stimulation. It is usual to apply mechanical, thermal, chemical and 

 electric stimulation. Experience has shown that of all these means 

 electricity is the most valuable, because it is subject to the greatest 

 number of variations in strength and in method of application. 

 Before entering upon a study of the response of irritable tissues to 

 electric stimuli it is essential to make a short study of the appliances 

 used. As many of these appliances have been used by the student 

 in the physical laboratory it will be taken for granted that he is 

 familiar with the principles involved in their use. 



1. Appliances. Two Daniell elements or cells; wires; contact key; 

 Du Bois-Reymond key; mercury key; commutator; 10 per cent, 

 sulphuric acid; copper sulphate, saturated solution; mercury. 



2. Experiments and Observations, (a) The Daniell Cell. Note 

 the four parts of the cell. Half-fill the outer receptacle of the cell 

 with the saturated copper sulphate solution. Put the copper plate 

 into the cell; half -fill the porous cup with the dilute sulphuric acid; 

 lower the zinc plate carefully into the cup. The plate is of com- 

 mercial zinc with its various impurities. 



(1) Observe the vigorous chemical action in porous cup. Express 

 the reaction in symbols. It is evident that the zinc will be quickly 

 consumed if allowed to remain in the acid, and this will be the case 

 whether or not the cup and zinc plate be made a part of an electric 

 cell, and whether the cell be acting or resting. 



(2) The amalgamation of the zinc. (See also Appendix, 4.) Lift 

 the zinc plate out of the acid, dip it into the mercury. The mercury 

 adheres to the zinc, mingles with the surface layer of zinc, forming 

 an alloy; with a brush or an old cloth one may rub the mercury over 

 the whole surface of the zinc plate the zinc is amalgamated. The 

 impurities of the zinc do not enter into the alloy. In this way only 

 the pure zinc which forms a part of the alloy is presented to the 



