24 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



muscle is composed. Electrical stimuli, on the contrary, are 

 applied easily, are readily controlled as regards their intensity, and 

 affect all the fibers simultaneously, thus giving a co-ordinated 

 contraction of the entire bundle, as is the case with the normal 

 stimulus. For electrical stimulation we may use the galvanic 

 current taken directly from the battery, or the induced or so-called 

 faradic current obtained from an induction coil. Under most 

 conditions the latter is more convenient, since it gives brief shocks, 

 the strength and number of which can be controlled readily. The 

 form in which this instrument is used in experimental work in 

 physiology we owe to du Bois-Reymond (1849-); hence it is 

 frequently known as the du Bois-Revmond induction coil. Experi- 



A B 



Fig. 7. Schema of induction apparatus. (Lombard.) b represents the galvanic 

 battery connected by wires to the primary coil, A. On the course of one of these wires 

 is a key (k) to make and break the current. B shows the principle of the secondary 

 coil, and the connection of its two ends with the nerve of a nerve-muscle preparation. 

 When the battery current is closed or made in A, a brief current of high intensity is 

 induced in B. This is known as the making or closing shock. When the battery current 

 is broken in A, a second brief induction current is aroused in B. This is known as the 

 breaking or opening shock. 



mental physiology owes a great deal to this simple and serviceable 

 instrument. A figure and brief description of the apparatus is 

 appended (Figs. 6 and 7). 



SIMPLE CONTRACTION OF MUSCLE. 



Experiments may be made upon the muscles of various animals, 

 but ordinarily in physiological laboratories one of the muscles 

 (gastrocnemius) of the hind leg of the frog is employed. If such 

 a muscle is isolated and connected with the terminals from an 

 induction coil it may be stimulated by a single shock or by a series 

 of rapidly repeated shocks. The contraction that results from a 

 single stimulus is designated as a simple contraction. In the frog's 

 muscle it is very brief, lasting for 0.1 second or less; but in this, 

 as in other respects, cross-striated muscular tissue varies in different 

 animals,* as is shown by the accompanying table, which gives an 

 idea of the range of rapidity of contraction. 



* Cash, "Archiv f. Anat. u. Physiol.," 1880, suppl. volume, p. 147. 



