PROTOPLASMIC MOVEMENT. 41? 



to muscles, we can now no longer doubt that changes of form 

 of their contractile particles go hand in hand with changes in 

 the amount of their water-contents, i.e. with the extent to which 

 they are swollen by imbibition. As can be proved, the con- 

 tractile, doubly-refracting bands of transversely striated mus- 

 cular fibres swell up during vital shortening by the imbibition 

 of fluid from the isotropic, non-contractile bands lying between 

 them, and on relaxation this fluid is given up again to the 

 latter. Vice versa, the characteristic shortening can be pro- 

 duced by artificially caused swelling of the doubly-refracting 

 discs of muscles, even when they are no longer excitable. The 

 same is the case with cilia. It is now a generally accepted rule 

 that anisodiametric, doubly-refracting organised animal and 

 vegetable structures, whether living or dead, tend to shorten on 

 the imbibition of water (swelling — Quellung) — often with very 

 great force and always in the direction of the optical axis. We 

 may assume that the proximate cause of the change of form of 

 inotagmata of the protoplasm (as of those of other contractile 

 substances) is a change of their water- contents, and thus look 

 upon the cause of contraction as a peculiar process of swelling 

 ( Quellungsvorgang) . 



Hofmeister ^ has already, starting from the changeability of 

 the imbibition condition of the protoplasm, looked for the cause 

 of its movement in periodical changes of the water-contents of 

 the smallest protoplasmic particles, and carried this theory out 

 thoroughly in an original manner. He assumed, however, 

 only volume- and not form-changes of the smallest particles, 

 which does not suffice to explain the great amount of the short- 

 ening or lengthening observable in many cases. He was not 

 then acquainted with the process of " swelling " which takes 

 place in the contraction of muscles. 



In so far as the process of contraction has been hitherto re- 

 ferred to a process observable in undoubtedly lifeless bodies 

 (e. g. connective-tissue fibres dried or hardened in absolute 

 alcohol) the further analysis of the mechanism must be left to 



^ W. Hofmeister, 'Die Lehre von der Pflanzenzelle,' p. 63, et seq., 1869. 



