CHAPTER IX 



MUSCLE 



IT is impossible to understand the general physiology of muscle and 

 nerve without some acquaintance with electricity. It would be out 

 of place to give even a complete sketch 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, it may be useful to recall the physical facts 

 involved. 



Batteries. The Daniell cell is perhaps better suited for physio- 

 logical work than any other voltaic element, although for special 

 purposes Bunsen, Grove, Le- 

 clanche, and bichromate of 

 potassium batteries may be 

 employed. Dry batteries are 

 very convenient for work in 

 which the current does not 

 need to be very constant, and 

 where it is only closed for a 

 short time. 



The Daniell is a two-fluid cell. 

 Saturated solution of sulphate 

 of copper is contained in an 

 outer vessel, and a dilute solu- 

 tion of sulphuric acid in a 

 porous pot standing in the 

 copper sulphate solution. The 

 latter is kept saturated by a 

 few crystals of copper sulphate. 

 A piece of sheet-copper, gener- 

 ally bent so as to form a hollow cylinder, dips into the sulphate of 

 copper, and a piece of amalgamated zinc into the contents of the 

 porous pot. Inside the 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 



615 



FIG. 203. DANIELL CELL. 



A, outer vessel ; B, copper ; C, porous 

 pot ; D, zinc rod ; D is supposed to be 

 raised a little so as to be seen. 



