108 THE NATURE OF THE 



EXPERIMENT. A nerve-muscle preparation from a Kana esculenta of moderate size 

 is arranged in a Pfliiger's myograph. The electrodes are placed on the nerve at 

 indifferent points, the proximal one at about 30 mm. from the cut end, which is held by 

 a thread, the distal at about 1 2 mm. from the muscle and 7 mm. from the proximal 

 one. The current is of one Daniell. Mercury keys are inserted in both the main and 

 the nerve circuit. As derivation-circuit (rheochord) I used in these and other experi- 

 ments three German-silver wires stretched backwards and forwards parallel to one 

 another on a board, and each I metre long and -5 mm. in cross-section. Contact of 

 one of the electrodes, which was movable, with the wire was brought about by 

 means of a pair of forceps, made on the principle of ordinary spring-forceps and 

 well nickel-plated, which rode on the wire. The blades of the forceps were thick 

 and heavy at their ends, so that they kept fast. At their other end the forceps carried 

 a small screw, by which the electrode wire was fixed. As the derivation-circuit wire 

 was carried well clear of the board, the forceps could be very easily applied at any 

 desired point on a wire, or transferred from one wire to the other. I cau recommend 

 this as a very practical arrangement. It appears to me to be both neater and more 

 certain than the mercury contact in du Bois-Reymond's rheochord. 



The following experiments were made for comparison. Firstly, the break-con- 

 tractions were compared with one another as to size when the current was opened 

 only in the nerve-circuit, (a) with unpolarisable and (6) with polarisable electrodes ; 

 secondly, when the current was opened only in the main circuit. There are thus 

 the following four cases : 



, . , , (a. Unpolarisable electrodes (i) 



A. Current opened in the nerve-circuit ... ft Poi ; risable ^ 



B. Current opened in the main circuit ... pal (4) 



"We shall first compare cases i and 2, and 3 and 4. Afterwards (see below) cases 

 I and 3, and 2 and 4 will also be compared. 



The following is the record of the experiments : 



first Break-contraction. 

 Experiment i : 



In case I no contraction up to 300 cm. derivation-circuit (rheochord wire). 



2 3 



3 contraction began at 275 



>, 4 3 



Experiment 2 : 



In case I no contraction up to 300 cm. derivation-circuit. 

 2 300 



3 contraction began at 260 ,, ,, 



4 4 



In experiment i the exciting current was ascending, in experiment 2 descending. 

 Two additional experiments, in which the conditions were exactly the same as in the 

 two first ones, gave the following results : 



First Break-contraction. 

 Experiment i : 



In case I contraction began at 2 85 cm. derivation-circuit. 

 2 no contraction up to 300 



,, 3 contraction began at 230 ,, 



.. 4 35 ., 



Experiment 2 : 



In case I no contraction up to 300 cm. derivation-circuit. 

 ,, a 300 



3 contraction began at 260 



4 4 



