14 Dr. J. B. Sanderson. The Time-relations of [May 1, 



II. " Photographic Determination of the Time-relations of the 

 Changes which take place in Muscle during the Period of 

 so-called ' Latent Stimulation.' " By J. BUR DON SANDERSOV, 

 F.R.S. Received April 17, 1890. 



It is now forty years since Helmholtz published his fundamental 

 experiments on the time-relations of muscular contractions. The 

 purpose of this investigation was to ascertain " the periods and 

 stages in which the energy of muscle rises and sinks after instan- 

 taneous stimulation ; " the word energy being defined as the " mecha- 

 nical expression of activity ; " and one of the most important con- 

 clusions of the author was that, in the muscles investigated by him, 

 contraction does not begin until nearly one hundredth of a second 

 after excitation. This interval has, by subsequent writers, been 

 called the period of " latent stimulation." 



Helmholtz subsequently (1854) showed, by experiments of surpass- 

 ing ingenuity, that during this period an electrical change of very 

 short duration occurs, which culminates at about one two-hundredth 

 of a second after excitation. The fact discovered by Helmholtz was 

 further investigated by Bernstein in 1866, with the aid of the repeat- 

 ing rheotome, and subsequently (1875) by du Bois-Reymond, whose 

 statement of the actual time-relations of the electrical response to an 

 instantaneous excitation of the gastrocnemius of the frog is embodied 

 in a curve which denotes that the muscular surface becomes negative 

 to the tendon about three thousandths of a second after excitation, 

 that this effect culminates at seven thousandths of a second, and that 

 it is immediately followed by a change of opposite sign, which 

 culminates at about ten thousandths. 



The statement enunciated above may be taken to represent the 

 present state of knowledge on the subject of the " negative variation " 

 or electrical response of muscle to an instantaneous stimulus ; but, as 

 regards the mechanical response, a great effort has been made of late 

 years to obtain a more accurate measurement of the period of latent 

 stimulation by methods founded on those originally employed by 

 Helmholtz, with the result that it has been shortened very consider- 

 ably. Two observers, viz., Professor Tigerstedt, of Stockholm, and 

 more recently Professor Yeo, F.R.S. , have, by improved methods, 

 obtained records from which they conclude that the duration of the 

 period is O005". Finally, Professor Regecsky, of Pesth, has, by 

 avoiding certain sources of error, obtained curves which lead him to 

 conclude that the mechanical response may begin " a-t the moment of 

 direct excitation" in other words, that the period of latent stimula- 

 tion does not exist. 



