24 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



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 ob- 

 tained 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-Reymond induction coil. Experimental physiology 



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 i, 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. 



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 isolated 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. 



