File:Exercises in practical physiology (1897) (14578402477).jpg

Identifier: exercisesinpract00wall (find matches)
Title: Exercises in practical physiology
Year: 1897 (1890s)
Authors: Waller, Augustus Désiré, 1856-1922
Subjects: Physiology Biochemistry
Publisher: London New York, N.Y. Bombay : Longmans, Green, and Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
l resistance, theP.D. ( Potential Difference ) at the two terminals is practicallyequal to the full E.M.F. of the cell (i.e., 1 Dan. or about Ilvolt), and the P.D. at any two points of the circuit variesdirectly as the resistance between these points. Thus the P.D.at two points of a muscle is ascertained by finding the resist-ance, r, at which it is balanced (i.e., no current through the V galvanometer) ; it is then equal to y-j—^. For example, if the balance is obtained with r =ohms, the muscle potential is r + E 250 ohms, and r + E = 7500250 7500 or -033 Dan. 26 EXERCISES AND DEMONSTRATIONS (16) Equipotential Lines. Dem. A Daniell cell, a du Bois key, galvanometer, a large flatdish of zinc sulphate, two pairs of amalgamated zinc elec-trodes. Fix the leading-in electrodes at H ; place one leading-off electrode midway between them. (1) Determine the equator 0 0 by shifting the other lead-ing-off electrode to positions at which no current passes thegalvanometer on closure of the key.
Text Appearing After Image:
Fig. 26. (2) Shift the electrode towards +, and on closure of thekey observe a current through the galvanometer from S to N,indicating + potential at this point. (3) Shift the electrode towards —, and on closure of thekey, observe a deflection from N to S, indicating — potential atthat point. IN THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 27 (4) Shift the first leading-off electrode nearer to —, and bysuccessive trials of shifting the second lead-off, find severalequipotential points, from which construct a curve. (5) Repeat the observation with the first leading-off electrodenearer to +. (Vide Human Physiology, p. 306). (6) Find equipotential curves near and far from one of thepoles, place the leading-off electrodes on any two points ofeach of these curves, and observe the galvanometer on closureof the key; or, more simply, take a pair of leading-off electrodesat a fixed distance from each other, and find positions in thefield at which more or less current passes in one or otherdirec

Note About Images