THE PHENOMENON OF CONTRACTION. 25 



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-Reyrnond ; hence it is frequently 

 known as the du Bois-Reymond induction coil. Experimental 

 physiology owes a great deal to this simple and serviceable in- 



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. 



strument. A figure and brief description of the apparatus are 

 appended (Figs. 6 and 7). 



Simple Contraction of Muscle. Experiments may be made 

 upon the muscles of various animals, but ordinarily in physiolog- 

 ical 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 a 

 general idea of the range of rapidity of contraction: 



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



