1 72 ITOW TO WORK 



they cannot be explains! by known laws. Any unprejudiced person 

 Avho thoroughly studies the movements and carefully thinks over the 

 facts of the case, will, I think, find himself compelled to admit that 

 they cannot be accounted for in the present state of our knowledge, 

 without assuming the existence of vital power. 



263. Of tlie Secondary Movements occurring in Living Beings. 

 Ciliary movement has been already referred to in p. 161, and mus- 

 cular contraction in p. 160. 



Of Molecular Movements. When any solid- matter in an exceed- 

 ingly minute state of division is suspended in a limpid fluid, every 

 one of the minute particles is seen to be in a state of active motion 

 or vibration in the neighbourhood of other particles. The cause of 

 these molecular movements has not yet been- satisfactorily explained, 

 and they have often been mistaken for vital movements. If some 

 bacteria developed in any decomposing water be exposed to a tem- 

 perature of 200 they are destroyed, but although quite dead, mole- 

 cular movements still occur. If however, the movements of the dead 

 particles be compared with those of living bacteria, a great difference 

 will be discerned. Probably many movements of particles occurring 

 in cavities in crystals are of the same nature. See p. 178. 



Movements of Granules within Cells. Y\\Q movement of insolu- 

 ble particles from one part of a cell to another, as occurs in the 

 radiating pigment-cells of batrachia (frog, toad, and newt), is proba- 

 bly due to alterations in the direction of the flow of fluid in the cells, 

 from the cavity of the cell towards the tissues, or from the surround- 

 ing tissue into the cell. If the capillaries were fully distended, 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 diminished, there would be, as is well known, a ten- 

 dency for the fluid in the surrounding tissue to flow towards the ves- 

 sels and pass into their interior. In this case the quantity of fluid in 

 the cells would become gradually reduced, and the insoluble particles 

 would become aggregated together, and would collect in those situa- 

 tions 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. 



