1902.] Photographic Records of the Response of Nerve. 



195 



meter, differ in form from the records of the muscle response. In the 

 former case the movement of the meniscus commences suddenly — the 

 velocity is maximal at the commencement— the change of direction is 

 sudden, and the end of the second phase is sudden also. It is quite 

 otherwise with the records of the electrical response of muscle or 

 nerve. There is great variety in them. The movement generally com- 

 mences gradually. Maximum velocity may occur early or quite near 

 the end of the first phase. The reversal of direction may be so sudden 

 as to form a cusp, or the curve may be flat-topped for 0*001 sec. or 

 0*002 sec. The second or electro-negative phase may be cut short, or 

 may exceed the first or electro-positive phase in magnitude. It may 

 end almost abruptly or tail off so gently that it is difficult to deter- 

 mine when it ceases. But so long as the conditions are unaltered the 

 same shaped curve is produced on repeating the experiment. 



These varieties among the records are therefore due to characteristic 

 peculiarities of the preparations. 



But the characteristic peculiarities of a preparation may depend on 

 the one hand upon its physiological state, and on the other upon 

 purely physical and experimental conditions. It is necessary there- 

 fore to trace the influence of these latter on the form of the records, in 

 order, by a process of elimination, to discover the results due to physio- 

 logical differences. 



I propose therefore in the present communication to show that it is 

 possible to obtain further information by applying to the derived 

 curves a process of interpretation based on purely physical grounds, 

 and shall avoid dealing with the physiological side of the question 

 except so far as may be necessary for the sake of clearness. 



The first statement of the problem is best made from the experi- 

 mental standpoint, and may be expressed briefly as follows* :— 



* \_Note, added April 10, 1902. — This is an expression from a purely physical 

 standpoint of the well-known physiological theory of which the experimental basis 

 is in brief : — 



1. Du Bois Beymond's demonstration that the excitatory process in nerve is 

 associated with electrical phenomena. 



2. The classical experiment of Helmholtz, showing that the excitatory process 

 in motor nerve, as judged by the time of the muscle response, is transmitted 

 ulong the nerve at a definite rate. 



3. Bernstein's proof, by means of his revolving rheotome, that the electrical 

 phenomena are transmitted in the form of a wave at the same rate. 



A great deal of work on the subject has been done with the revolving rheotome 

 by Hermann, Bornttau, Hering, and others. 



Professor Gotch and I have discontinued the use of the revolving rheotome, 

 because, in the first place, the condition of the nerve is liable to be altered by the 

 rapid series of excitations; in the second place, because the after-effect of each 

 ■excitation is mixed up with those of succeeding ones ; and in the third place, 

 because the capillary elctrometer is far more sensitive. 



It is this greater sensitiveness that has enabled me to push the investigation so 

 much farther than has hitherto been attempted.] 



p 2 



