( 46 ) 



A small pendulum with a fixed turning-point, of which the short 

 beam points upwards to a height of 6 cM., bears on the head of that 

 short arm a handled glass-tear, whilst the other longest arm, 15 eM. long, 

 is provided with a small, movable weight, in consequence of which 

 the moment of that lever-beam is variable. By this way the force with 

 which the head of the glass-tear hits the object, can be made variable. 

 In order to enlarge the living force of the falling object, the pendulum 

 may be given different initial amplitudes. On a scale along which 

 the longest lever moves, this height of falling is expressed in degrees. 



The muscle to be examined is by means of its two tendons 

 attached to a somewhat rough surface, here a hard cork-plate, to 

 prevent removal of the muscle by the falling, tapping object. It 

 is advisable in this way to determine the hardness of a muscle under 

 isometric conditions, for, when the muscle is examined under isotonic 

 conditions, the data are getting far less trustworthy, as : 1. in 

 shortening the muscle, the point that is to be touched, bj r not shor- 

 tening changes its place and can only be found back by marking 

 it beforehand with colouring matter; 2. the weight necessary for 

 the stretching seems to make the differences in hardness smaller. 



The number of times that the glass-tear is reflected by the muscle 

 before it is at rest, is determined either acoustically or by means 

 of photography. The photographic registration has this advantage that 

 at the same time the width of the reflections can be followed. 



The photographic registration takes place as follows : the light of 

 an arc-lamp of 220 volt and 10 ampère is by a condenser more or 

 less pressed together into a cone of rays having its focus in a dia- 

 phragm. This focus in its turn serves as a source of light and pro- 

 cures by means of a biconvex lens the parallel bundle of rays 

 emitted. This bundle reaches the removable slit of a small box which 

 in its opposite side is provided with a cylinder-lens of Garten. 

 The light that has entered through the slit, is by the cylinder- 

 lens, which is graduated, nipped together to an horizontal line of 

 light, which falls through another slit into a second larger box 

 on a drum that is in rotatory motion and to which sensitive bromide- 

 paper of Dr. Schaefelen is fixed. The box containing the drum is 

 impenetrable to light by means of light-free axes. This drum is 

 moved on by a clock, as it is used in the telegraphic Morse-apparatus. 

 Between cylinder-lens and the larger box is placed the long beam 

 of the lever of the sclerometer which during its movements removes 

 a silhouette on the sensitive silver-paper. 



The following experiment was made : M. sartorius of Rana 

 temporaria is alternately passed through by an electric current, arising 



