66 Proceedings of Royal Society of Edinburgh. [sess. 
the other binding screw (X) from the support. During the revolu- 
tion of the drum the pin S touches the spring T and thus closes 
the circuit. The duration of the contact between the pin and the 
spring can be altered by adjusting the position of the spring, or in 
other words, the time-interval between the closing and the opening 
of the circuit can thus be regulated. The secondary coil is so 
adjusted as to obtain maximal stimulus both on making and 
breaking. Now, it is evident that during the revolution of the drum, 
as soon as the pin S touches the spring T, the circuit being com- 
pleted, the muscle stimulated by the “make” shock tends to 
contract, but is prevented owing, at the same time, to the arma- 
ture (K) being firmly held by the electro-magnet. Thus isometric 
condition of the muscle is attained. Quickly following this raising 
of the tension of the muscle the circuit is broken, and the “ break J? 
shock again stimulates the muscle, which rapidly contracts with 
freedom, ; the electro-magnet having now ceased to act. 
Thus we are able to record on the smoked surface of the 
revolving drum the character and velocity of the contraction of 
the muscle under such modified condition. Detailed account of a 
series of observations will be published in a subsequent paper, but 
it may be briefly mentioned here that by this means a greater 
velocity of contraction is obtained and the rate of work is also 
increased. 
2. For isotonic contraction the electro-magnet is thrown out of the 
primary circuit, and the lever is freed from the armature by taking 
out the hook attached to the string. The muscle is fixed as in the 
former case, and the end of the elastic band which is attached to 
the lever is brought very close to the pivot, so that during con- 
traction of the muscle there will be very little extension of the 
elastic band. The muscle is stimulated by •“ make ” or “ break ” 
shock — preferably the latter — using an ordinary key for this 
purpose, and the characteristic myogram is obtained on the smoked 
surface. 
3. For isometric contraction the elastic band (0) is replaced by a 
steel (spiral) spring, fig. 2, III., one end of which is fastened to 
the brass clamp B', and the other hooked on the lever so that the 
muscle, when stimulated, shortens against great resistance. By 
adjusting a screw connected with the spring the initial tension of 
