MOTION IN ANIMALS AND PLANTS. 



339 



screen together, in such a way that they are in synchronic relation to 

 each other (photograph 3, PI. I). 



The experiment may be further yaried by altering the seat of exci- 

 tation from /' to /''. You thus obtain a photographic record which 

 represents what happened at d in the unligatured muscle. If the 

 muscle Is in a normal state, this is an exact reversed counterpart of 

 photograph 2. 



If instead of placing the ligature half way between j> and d^ we 

 place it close to the distal electrode d^ the proximal ma}^ then be placed 

 in a succession of experiments at different dis- 

 tances from the seat of excitation without altering 

 the form of the recorded variation; the time at 

 which it begins depends in each case on the dis- 

 tance of the proximal contact from the seat of 

 excitation.^ 



In all of these instances the ligature acts as a 

 block. Without interfering with the condition 

 of any other parts it kills the part which it grasps 

 and makes it incapable of transmitting the excited 

 state from the living structural elements on one 

 side to those on the other; but if we compare the 

 condition of the unexcited preparation immedi- 

 ately before and after the application of the liga- 

 ture we find evidence that breach of continuity 

 of function is not the only effect produced by it. 

 If the one contact is placed on the ligatured part 

 it is found that, irrespectively of any excitation, 

 there exists a large difference of potential between 

 the contacts, which may amount to four or six 

 hundredths of a volt. 



THE MUSCLE CUERENT. 



Now it is easy to prove that this difference is 

 Diagram 4. not due to breach of continuity, for if j^ou shove 



Explanation of Diagram 4. — The horizontal line is that of equipotentiality of the 

 two surfaces of contact p and d. The curve P' expresses the relative negativity 

 (negative difference of potential) of the surface p; the curve D', the corresponding 

 relative negativity of the surface d. S is a curve of which the brdinates are the alge- 

 braic sums of the correspondinsr ordinates of P^ and D\ S is the photographic 

 curve which expresses S'; P^ is the photographic curve which expresses P. The 

 numbers under the horizontal line indicate hundredths of a second. The distance 

 1 1' expresses the time taken by the wave in its progress from p to d. 



^ An experiment of this kind is by far the most exact method which we possess of 

 measuring the conduction-rate in muscle. This rate is most correctly expressed by 



the quotient: 



Difference between the distances 



Difference between the times 

 as measured in two experiments in which the distances are different. 



