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



mechanical energy of shortening is elevation of temperature. Cooling 

 has the opposite effect. 



Particularly instructive is the thermal contraction of fibrillar con- 

 nective tissue, on account of its similarity to muscular movement, 

 even with regard to details. This tissue, like muscle, consists of 

 doubly refractive fibrils and of an inter-fibrillar singly refractive 

 isotropic substance. The fibrils have about the same dimensions 

 as muscular fibrils, and, for the rest, show, in their optical and 

 mechanical behaviour under various influences, a great likeness to 

 muscular fibrils, especially to the doubly-refractive sarcous elements. 

 In tendons and many membranes the fibrils, as well as those of 

 most muscles, are arranged into bundles, all, or nearly all, parallel 

 to each other. For this reason such objects are extremely well fitted 

 for a closer examination of the phenomena of movement. The most 

 suitable material I know is furnished by the catgut string of a violin, 

 which consists chiefly of such bundles, running in steep spiral lines 

 round the longitudinal axis of the string. Such a string is dis- 

 tinguished from the greater number of naturally occurring objects by 

 its very regular cylindrical shape and its elasticity. On these pro- 

 perties is based its suitability for musical purposes, especially for 

 the so-called " perfect fifth " (" Quintenreinheit ") . 



The Muscle-Model. With the aid of such a string we can compose 

 a model which in a simple way explains how in the muscle me- 

 chanical energy of contraction may result from heat without any 

 perceptible rise of the average temperature of the muscle. 



The following sketch (fig. 1) presents this model of the muscle dia- 

 grammatically simplified : 



A piece of an E string of a violin, about 5 cm. long and previously 

 swollen in water, is fastened to the end, a, of the short rigid arm of 

 a steel rod, a&, while the upper end of the string is fixed on 

 the shorter arm of the lever, H, turning round the horizontal axis, c. 

 To this string different tensions may be imparted by weights 

 (J, cZi), or springs, acting upon the lever, and since the point of appli- 

 cation of the string may be changed at will, its contraction, with ail 

 the conditions of isometry, isotony, and auxotony may be examined. 



Bound the string, but without touching it, runs for a length of 

 about 20 mm., and in about twenty curves, a spiral of thin platinum 

 wire. Its ends may be connected by means of two binding-screws 

 of the ebonite or ivory piece, /, with the two wires coming from the 

 poles of a Grove or Bunsen battery of three or more cells. The rod, 

 ai, bearing lever, string, and spiral wire, is placed in a glass of 

 about 50 c.c. content, filled with water of about 55 60 C., and closed 

 at the top by an ebonite lid. Through an aperture in the lid, a 

 thermometer is placed in the water in such a position that it will 

 remain at a distance of about 1 cm. from the spiral wire. 



