546 Dr. A. D. Waller. Comparative Power of [June 24, 



consisting of the responses while the muscle is replaced in normal saline. 

 The solutions are changed by being run off through a tap and run in from 

 a pipette, care being taken that the volume of fluid is always the same. 

 The induction currents are kept going automatically throughout an experi- 

 ment, excepting during the short periods required for changing the solution. 

 The apparatus used for this purpose consists of : (1) a Berne coil fed by a 

 2-volt accumulator ; (2) a Brodie clock with interruptions set at six per 

 minute ; and (3) a relay key, i.e. that shown by G-. K. Mines at the July, 

 1908, meeting of the Physiological Society. 



As a general rule of procedure in any comparison between the effects upon 

 two muscles L and B of two solutions A and B, a first comparison is made 

 between the effects of A on L and of B on B, and a second comparison of 

 the effects of B on L and of A on B. Each complete experiment thus 

 comprises two pairs of simultaneous trials of two solutions in reversed order of 

 action, and constitutes an experimentum critcis in the strict sense of the term. 



Electrical excitation of the muscles while immersed in the experimental 

 solutions — in spite of the fact that the induction currents are in large 

 measure short-circuited by the solution — was systematically adopted in 

 preference to excitation of the muscle after the solutions had been run off, 

 because it affords a more complete picture of the gradual effects of such 

 solutions. Currents of sufficient strength are taken to give maximal excita- 

 tion in spite of the derivation. 



The diameter of the muscle vessel was slightly less than 3 cm., so that 

 30 c.c. of fluid gave in it a column about 5 cm. long, more than sufficient to 

 ikeep the muscle wholly immersed. 



Double Myograph to test Action of Substances in Solution. 



