xx MOTIONS OF THE PROTOPLASM. 



coloured grains (of chlorophyll) and other small masses and corpuscles con- 

 tained in the cavity, are seen to be moved along the inside of the cell- wall 

 in a constant and determinate direction. This phenomenon appears to be 

 of very general occurrence in the vegetable kingdom, although the movement 

 does not always go on with the same regularity as in the instances cited. 

 It is obviously due to a layer of protoplasm on the inner surface of the 

 cell-wall, which enters into a peculiar flowing or undulating motion and 

 trails the passive corpuscles along with it; but how the motion of the 

 protoplasm itself is produced is not at all understood. 



Motions are also observed in animal protoplasm ; cells in form of nucleated 

 protoplasm-masses of irregularly stellate or jagged outline, which lie in 

 the areolar tissue and are called connective tissue-corpuscles, and similar 

 bodies in the substance of the cornea, have been noticed slowly to change 

 figure whilst under observation (in the tissues of the recently killed frog), 

 shrinking in at one part of their uneven contour and extending their soft 

 substance at another. The effect seems to be due to a contractile property 

 of the protoplasm comparable to the contractility of muscular substance ; 

 for Kiihne* has found that the substance of these protoplasm bodies con- 

 tracts under the electric stimulus, and contractions may be excited in the 

 corneal cells through the medium of fine nerves which are distributed to 

 them, and this both by mechanical and electrical stimulation. Now the soft 

 transparent matter named te sarcode " which constitutes the bodies of the 

 amoeba and actinophrys, and the animal part of the foraminifera and 

 other allied organisms of simple nature, exhibits similar retractile and 

 extensile movements, and may also be made to contract by electrical excite- 

 ment ; and accordingly it is reckoned as an example of protoplasm by some 

 recent observers of authority and designated by that name. It is further 

 to be noted, however, that the varied movements of the amoebine animals 

 are very generally accompanied by a flowing of fine particles to and fro in 

 their pellucid substance, as if there were a thinner and more diffluent por- 

 tion confined within the more firm exterior part. The movement of the 

 fluid matter, and consequent flow of the particles carried by it, have been 

 ascribed by some observers to an impulse caused by the contractions of the 

 firmer portion, but there are cases in which this explanation is hardly 

 sufficient, and the point remains in doubt. 



To the same class of phenomena are probably to be referred the remark- 

 able movements observed in the pigment-cells of the frog's skin, which have 

 been so lucidly investigated by Professor Lister. t In these ramified cells 

 the dark particles of pigment are at one time dispersed through the whole 

 cell and its branches, but at another time they gather into a heap in the 

 central part, leaving the rest of the branched cell vacant, but without 

 alteration of its figure. In the former case the skin is of a dusky hue ; in 

 the latter, pale. The phenomenon is probably due to some kind of motion 

 of the protoplasm, although it must be admitted that Mr. Lister has 

 adduced arguments of considerable weight to prove that there is some 

 impulse operating directly on the particles, and that they move indepen- 

 dently of the surrounding matter, which he considers to be fluid. Like the 

 movements of the protoplasm, the aggregation of the pigment molecules can 

 be excited through the nerves, both mechanically and electrically. 



Lastly, the pale blood-corpuscles and other similarly constituted cells of 



* Untersuchungen iiber das Protoplasma und die Contractilitafc. 1864. 

 t Phil. Trans. 1858. 



