March 28, 1895J 



NA TURE 



=^21 



question for us. If we examine the optic properties of con- 

 tractile fibrils, with the aid of the polarising microscope, we 

 find that all of them are double-refractive, with one optical 

 axis parallel to the direction of contraction. 



This general occurrence of double-refracting power is the 

 more indicative of relations lo contractility, since non-contrac- 

 tile cells, as a rule, lack double refraction, even where we meet 

 with a fibrillar structure, as in the axis-cylinder of a nerve- 

 fibre. 



Our conjecture gains, I believe, a very high degree of prob- 

 ability by the following series of observations. 



In the first place, the fact that contractility and double 

 refraction in the course of ontogenesis always appear at the 

 same time, e.g. in the heart of the chick, on the second day of 

 incubation ; in the muscles of the trunk and skin on the fifth or 

 sixth day ; in the muscles of the taiU of tadpoles when the 

 length of their body is 3 to 4 mm. ; in the muscles of the stalk 

 of Vorticella, and in cilia so soon as these organs become 

 visible. 



-Vnother evidence seems to me to be afforded by the be- 

 haviour of the striated muscles. Here the fibrils consist of the 

 doubly-refiactive sarcous elements and the singly-refractive 

 material which joins these, the two alternating regularly. The 

 two are wholly diJTerent as regards their optical, mechanical, 

 and chemical properties ; and these properties, moreover, 

 during contraction, change in an opposite way. Hence the 

 functions of the two must be of a different kind. And since 

 the changes of form, volume, &c., of the doubly-refractive 

 parts during contraction prove that in each case there parts 

 must be the seat of contractile power, the single-refractive 

 junctions will most probably have another function. We will 

 come back to these changes further on. 



A third evidence is alTorded by the observation that the 

 specific force of contraction in different muscles is, in general, 

 greater, the better developed the power of double refraction, 

 comparison, of course, in each respect being made with parts of 

 the same thickness. 



In the development of the pseudo-electric organs of Kajii 

 ')Ut of striated muscular fibres, one of the signs of the in- 

 cipient change of structure and function is the vanishing of 

 double refraction in the sarcous elements. In an early stage 

 of development this vanishing is, with Raja clavata, the very 

 lirst and the only sign that the fibre is about to be transformed 

 trom a contractile into an electric organ. 



But particularly significant seems to me to be the behaviour 

 of the obliquely striated muscles of Molluscs and other Inveite- 

 brata. Here the doubly refractive fibrils do not run parallel 

 to the axis of the fibre, but describe spiral lines round it : 

 and during a contraction the steepness of the curves decreases, 

 ■io that the angle formed by the longitudinal axis of the fibril 

 and the longitudinal axis of the fibre may increase from 5' in 

 ho relaxed state to 60', and even more, in a state of powerful 

 contraction. But the optic axis of the fibril, instead of assum- 

 mg, in this case, a more oblique position also, as might be ex- 

 pected on morphological ground'-, remains parallel to the longi- 

 tudinal axis of the fibre, and consequently to the direction of 

 shortening of the fibre. Hence it is not the morphological axis 

 of the fibrils, but the optical axis of their doubly refractive 

 constituents, which coincides with the direction of the contract- 

 ing force. 



CoHtraclilily a General Property of Doubly Refractive 

 Bodies. — More than a score of years ago I pointed out the fact 

 that even non-muscular elements, elements not possessing 

 irritability in the physiological sense of the word, nay, even 

 lifeless, unorganised elements which are uniaxial doubly 

 refractive, may, under certain influences, contract in the 

 direction of the optical axis, all thickening at one time, ard 

 contracting with a force and quickness and to an extent 

 rivalling that of muscles, if not surpassing it. Instances 

 of this are the fibrils of the connective tissue, of the tendons, 

 and of the cornea, and otheis. The same contractile power 

 was found by von ICbner in a great many other doubly-refractive 

 histological elements, nay, even in substances capable of 

 absorption and thereby made doubly refractive, ,-. j-., dried col- 

 loid membranes ; and finally by Hermann, in fibrils of fibrin. 



I have in this «ay shown that singly refractive, or only 

 feebly doubly refractive histological elements, such as the fibies 

 of elastic tissue, obtain, in the same w.ay as caoutchouc, the 

 power, when made doubly refractive by extension, of contract- 

 ing under certain influences, and further that the force of 



shortening will generally be greater in proportion to the 

 amount of the double refraction thus artificially produced. 



Since, according to Mitscherlich's discovery, similar changes 

 of form may be observed in doubly refractive crystals, we have 

 apparently to deal with a property pertaining to all doubly 

 refractive bodies as such. 



Heat as a General Cause of Contraction of Doubly Refractive 

 Elements. — Now, the influence which in all these cases is able to 

 evoke the mechanical energy of shortening is elevation of tem- 

 perature. Refrigeration has the opposite effect. 



Particularly instructive is the thermal contraction of the 

 fibrillar connective tissue, on account of its similarity to 

 muscular movement, even with regard to details. 



In tendons .and many membranes the fibrils, as well as 

 those of most muscles, are arranged into bundles, all, or nearly 

 all, parallel lo each other. For this re.ason 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 strings of violins, which chiefly consist of such 

 bundles, running in steep spiral lines, round the longitudinal 

 axis of the string. They are distinguished from the 

 greater number of naturally occurring objects by their very 

 regular cylindrical shape and their elasticity. < 'n these 

 properties is based their suitability for musical purposes, 

 especially for the so-called "perfect fifth" (" Quintenrein- 

 heit"). 



The Muscle- I^PoJel. — With the aid of such a string we can 

 compo-e a model which in a simple way explains how in the 

 muscle mechanical energy of contraction may result from heat 

 without any perceptible rise of the average temperature of the 

 muscle. 



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

 previously swollen in water, is fastened to the end of the short 



IT 



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NO. 



1326, VOL. 51] 



Fig. I. 



rigid arm of a steel rod, while the upper end of the string is 

 fixed to the shorter arm of a lever, turning round an horizontal 

 axis. 



To this string different tensions may be imparted by weights 

 or springs, acting upon the lever. 



Round 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. The ends of this may be 

 connected with the two poles of a Grove or lUinsen 

 battery of three or moic cells. The rod, bearing the lever 

 string and spiral wire, is placed in a glass of about 50 c.c. 

 contents, filled with water of about S5-'6o' C, and closed at 

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



