PRELIMINARY DATA 697 



muscular fibre more than it does a nerve-fibre or a gland-cell or an 

 epithelial scale. The properties common to all muscle make up the 

 general physiology of muscular tissue. 



A nerve-fibre is at first sight very different from a muscular fibre. 

 It has diverged more widely from the primitive type of undiffer- 

 entiated protoplasm, but it retains, in common with the muscle- 

 fibre, susceptibility to stimulation, or excitability, the capacity for 

 growth, and to a limited extent the capacity for reproduction; and 

 while it has lost the power of contraction or contractility, it has 

 developed in a higher degree than any other tissue the power of 

 conducting the excited state. This inheritance of primitive pro- 

 perties, retained alike by both tissues, is the basis of the general 

 physiology of muscle and nerve. 



The electrical organ of Torpedo or Malapterurus is inter- 

 mediate in some respects between muscle and nerve, and has 

 properties common to both. In the gland-cell the chemical powers 

 of native protoplasm have been specialized and developed. Con- 

 tractility has been, in general, entirely lost ; but excitability remains. 

 The idea that certain common en- 

 dowments find expression in the 

 action of muscle, nerve, electrical 

 organ, gland, etc., in the midst 

 of all their apparent differences, is 

 the basis of the general physiology 

 of the excitable tissues. 



It is imposeible to understand the 

 general physiology of muscle and Fig . 2I9 ._ Danie ii Cell. A, outer vessel; 

 nerve without some acquaintance B, copper; C, porous pot; D, zinc rod; 

 with electricity. It would be out of D is supposed to be raised a little so as 

 place to give even a complete sketch to be seen, 

 of this preliminary but essential 



knowledge here; and the student is expressly warned that in this book 

 the elementary facts and principles of physics are assumed to be part 

 of his mental outfit. But in describing some of the electrical apparatus 

 most commonly used in the study of this portion of our subject, and 

 which are employed in the Practical Exercises, it may be useful to recall 

 some of the physical facts involved. 



Batteries. The Danicll cell is perha*ps better suited for physiological 

 work than any other voltaic element, although for special purposes 

 Grove, Leclanche, bichromate of potassium or dry batteries may be 

 employed (p. 195). Storage batteries or current from the street supply 

 may also be used. 



Inside the Daniell cell the current (the positive electricity) passes 

 from zinc to copper; outside, from copper to zinc. The copper is called 

 the positive, the zinc the negative, pole. When the current is passed 

 through a tissue, the electrode by which it enters is termed the anode, 

 and that by which it leaves the tissue the kathode. The anode is, 

 therefore, the electrode connected with the copper of the Daniell's cell; 

 the kathode is connected with the zinc. 



Potential Current Strength Resistance. We do not know what 

 in reality electricity is, but we do know that when a current flows along 



