THE PRODUCTION OF ENERGY IN MUSCLE 



101 



If an electric current is permitted to pass through it, it is moved laterally in a line 

 parallel to the poles, i.e., perpendicularly to the lines of force passing between the 

 poles of the magnet. These deflections take place to either side in accordance 

 with the direction of the current. Contrary to the d'Arsonval galvanometer, the 

 deflections of this string are not mere twists but actual lateral deviations which can 

 be increased and decreased by varying the tension placed upon the string. Know- 

 ing this tension, or, in other words, the resistance of the string, the strength of 

 the current causing its deviations, may be calculated directly from the size of the 

 deflections. The string galvanometer permits of a freedom of motion which the 

 ordinary forms of galvanometer cannot attain, although the actual sensitiveness 

 of the latter is no doubt greater than that of the former. Thus, its chief character- 



Fio. 56. EINTHOVEN'S STRING GALVANOMETER, AS MODIFIED BY CUNNINGHAM, 



WILLIAMS AND HINDLE. 



The front-cover has been removed to show the position of the string between the 

 poles of the magnet. The connecting posts lie behind the hood containing the string. 



istic is its speed of reaction which enables it to follow the electrical variations with 

 an almost immeasurable exactness. 



A third instrument which is sometimes used for the detection of electrical cur- 

 rents of animal origin, is the capillary electrometer (Lippmann, 1877). A glass tube 

 is drawn out at one end into a tube of capillary size and is filled with mercury up to 

 and beyond the point of entrance of a copper wire (A). This tube is then placed 

 vertical and is made to dip into a cup-shaped receptacle which is filled with mer- 

 cury and is pierced by a copper wire (B). A small quantity of dilute sulphuric acid 

 is now placed over the mercury in the cup. If the capillary is of proper size, the 

 mercury does not flow out, but is held at a definite level. By compressing a small 

 rubber bulb which is connected with the upper end of this tube (P), the mercury 

 is then forced downward and upward a number of times until the lower lumen 

 of the capillary tube is completely filled with the acid. The level of the mercury or 

 meniscus (Jtf) is adjusted under the objective of a microscope (L) ; in fact, it may 

 be projected upon a screen or upon sensitive paper. If an electrical current is now 



