422 Prof. Th. W. Engelmann. [Mar. 14, 



sinking closes the circuit of the spiral by dipping in mercury, and 

 breaks it again when rising, contraction and relaxation of the string 

 will alternate regularly for hours, just as with a beating heart. 



The movements may be inscribed on a rotating cylinder. We 

 then obtain curves of the same character as contraction -curves of 

 muscles (fig. 2). 



FIG. 2. 



Such a chordogram presents, like a myogram, three periods, viz.: 



1. A period of latent energy, the duration of which, just as with 

 the muscle, decreases with the increasing energy of the stimulus (-i.e., 

 with the intensity and duration of the electric current), with rising 

 temperature and with decreasing load. 



2. A period of augmenting energy, in which contraction takes 

 place with a rapidity, first increasing, afterwards diminishing, the 

 contraction being, within certain limits, more rapid and larger in 

 extent the stronger the stimulation. 



3. A period of declining energy, in which the string relaxes with a 

 gradually decreasing rapidity. 



Further Comparative Researches on the Thermal Contraction of Life- 

 less Doubly Refractive Bodies and the Physiological Contraction of 

 Muscle. The points of resemblance between our model and a muscle 

 extend much further yet, and amongst other to peculiarities which 

 seem to bear important testimony to the identity of the mechanical 

 process in the two cases. 



Such a resemblance I find, in the first place, in the fact that the 

 strength of the shortening power, developed Itij a certain stimulus, 

 increases with the load within certain limits. Both muscle and string 

 present the paradoxical phenomenon that, under a stimulus of equal 

 energy, heavier weights may be lifted higher than lighter ones. 



Adolf Fick first detected this surprising fact in the muscles of 

 Ancdonta ; and Rudolf Heidenhain, almost at the same time, observed 

 it in the striated muscle of Yertebrata. It has been generally con- 

 firmed, and seems to hold good for all kinds of muscles. 



Neither the chemical nor the electrical hypothesis of the origin of 



