1895.] On the Nature of Muscular Contraction. 419 



sarcous elements. In an early stage of development this vanishing 

 is, with Raja clavata, the very first and the only sign that the fibre is 

 about to be transformed from 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 Invertebrata. 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, so that the angle formed by the 

 longitudinal axis of the fibril and the longitudinal axis of the fibre 

 may increase from 5 in the relaxed state to 60, and even more, in a 

 state of powerful contraction. But the optic axis of the fibril, 

 instead of assuming, in this case, a more oblique position also, as 

 might be expected on morphological grounds, remains parallel to the 

 longitudinal 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 contracting force. 



Contractility 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 

 doubly refractive and uniaxial, may, under certain influences, contract 

 in the direction of the optical axis, all thickening at one time, and 

 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 

 connective tissue, of the tendons, and of the cornea and others. 

 The same contractile power was found by von Ebner in a great many 

 other doubly refractive histological elements, nay, even in substances 

 capable of imbibition and thereby made doubly refractive, e.g., dried 

 colloid membranes; and finally by Hermann in fibrils of fibrin. 



I have in this way shown that singly refractive, or only feebly 

 doubly refractive histological elements, such as fibres of elastic 

 tissue, in the same way as caoutchouc, obtain the power, when 

 made doubly refractive by extension, of contracting under certain 

 influences, and further that the force of shortening will generally be 

 greater iii 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 appa- 

 rently 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 



* Th. W. E., "Die Blattersckichfc der electrischen Organe ron Raja in ihren 

 genetischen Beziehungen," &c., ' Pfliiger's Arcliiv,' Bd. 57, 1894, p. 149. 



2 H 2 



