APPARATUS FOE PHYSIOLOGICAL USE. 247 



but can determine the intervals of time which elapse 

 between the opening and closing of the two sets of valves, 

 on the due working of which, the efficiency of the organ as 

 a pumping mechanism very principally depends. 



I now come to my last illustration, and I have put it last, 

 because I attach more importance to it, than to the others ; 

 for it involves a physiological experiment of fundamental 

 importance. I have prepared a muscle, the calf-muscle of a 

 frog, which was killed immediately before the lecture. The 

 muscle, although the frog of which a while ago it formed 

 part is dead, is itself living, i.e., it still enjoys the same 

 power of contracting, though in diminished completeness, 

 that it possessed when still part of a living organism. 

 Attached to the muscle is its motor nerve, which has also 

 been carefully prepared. Probably most of those present 

 are aware that when the motor nerve leading to a muscle 

 is interfered with so as to become excited or irritated, 

 the muscle contracts. If the excitation is of an instan- 

 taneous nature, such as is produced in this instance by 

 the passage of a single induction shock from this induction 

 machine, a single and apparently instantaneous shortening 

 of the muscle takes place, which if the tendon of the 

 muscle were still attached to the foot, would suddenly 

 extend it. As you will be able to see after the lecture 

 more distinctly, the end of the muscle nearest the knee 

 joint is immovably fixed to a block of cork ; the tendon 

 (i.e., the Tendo Achilles) is attached by a silk cord to 

 a lever so arranged, that when it is acted upon by the con- 

 tracting muscle, the receiving tympanum c, is pressed upon. 

 By the n^echanism with which you are now familiar, the 

 motion thus communicated is transmitted to the recording 

 tympanum d, and written by it on the blackened surface of 

 the revolving cylinder. 



The cylinder revolves forty times in a minute. Its cir- 

 cumference is twenty inches, consequently the rate of hori- 

 zontal motion of the surface of the paper is 800 inches per 

 minute or 13*3 inches per second. In connection with the 

 cylinder there is an arrangement, by which, each time that 

 a certain point in its circumference touches a trigger, the 

 primary circuit of the induction apparatus is closed, so that 

 a so-called " closing " shock is sent through the nerve, by 

 means of a pair of platinum electrodes which are in contact 



