1865.] Movements of Granules within Cells. 233 



In the immediate vicinity of ciliated cells are sometimes observed cells 

 with open mouths, out of which mucus and various substances, formed or 

 secreted in the interior of the cell, pass. In the formation of these pro- 

 ducts, nutrient matter from the blood, after passing through the attached 

 extremity of the cell, is probably absorbed by the living matter. At the 

 same time the outermost portion of the latter becomes converted into the 

 peculiar contents of the cell, and thus the formed matter which has been 

 already produced becomes pushed towards the orifice. This is explained by 

 the drawing; and I think that the movements of cilia are brought about by 

 a somewhat similar series of changes, in which the germinal or living matter, 

 usually termed " nucleus," plays the active and most important part. 



Movements of granules within cells. The movement of insoluble par- 

 ticles from one part of a cell to another, as occurs in the radiating pigment- 

 cells of Batrachia, is probably due to alteration in the direction of the flow 

 of fluid in the cells, from the cavity of the cell towards the tissues, or 

 from the surrounding tissue into the cell. If the capillaries were fully dis- 

 tended, fluid would permeate their walls and would pass into the cavity of the 

 cells, in which case the insoluble particles would gradually become diffused 

 and would pass into all parts of the cell ; while, on the other hand, if the 

 capillaries were reduced in diameter, and the lateral pressure upon their 

 walls reduced, there would be, as is well known, a tendency for the fluid in 

 the surrounding tissue to flow towards the vessels and pass into their 

 interior. In this case the quantity of fluid in the cells would be gradually 

 reduced, and the insoluble particles would become aggregated together and 

 would collect in those situations where there was most space, as in the 

 central part of the cell, around the nucleus. Moreover, in the last 

 case, the flow of fluid, which constantly sets towards the nucleus, would 

 be instrumental in drawing the particles in this same direction, while if 

 the cell contained a considerable proportion of fluid, the currents would 

 pass between the particles without moving them. Evaporation, as it occurs 

 after death, causes concentration of the insoluble particles towards the 

 centre of the cells. 



On the other hand, the changes in the pigment-cells of the frog have 

 been considered by Professor Lister to be due to vital actions, and he 

 agrees with "Wittich and others that they are under the immediate control 

 of the nervous system. Indirectly of course they are, but I do not think that 

 any experiments have proved satisfactorily that the nerves exert any direct 

 influence upon the movements of the particles in these cells. It is well 

 known that the nerves govern the calibre of the vessels, and thus influence 

 the amount of fluid in the surrounding tissue, and in this indirect manner 

 they doubtless affect the movements of the particles in the cells. The 

 reader will find a full account of Prof. Lister's experiments, and the argu- 

 ments deduced from them, in his paper " On the Cutaneous Pigmentary 

 System of the Frog," published in the Philosophical Transactions for 1858. 



Muscular movement is illustrated by the figures to which I now refer, 



