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posure to light, by death of the animal, and by sudden section of 
the nerve going to tho skin — while darkness and irritation of the 
nerve or skin causes diffusion. Sudden amputation of a limb pro- 
duced at first diffusion, followed by the concentration of death. 
These movements of the pigment molecules are peculiarly vital, 
and altogether independent of the cell wall or nucleus. The cell 
wall is stationary, and acts only as a sac or investing membrane 
around the moving particles, while the concentration of these about 
the nucleus is purely accidental, and frequently occurs in other parts 
of the cell. The author had seen these molecules himself, as Mr 
Lister describes them, streaming out to and returning from the cir- 
cumference under the influence of the stimuli referred to, where no 
cell nor nuclear action could be thought of. 
bth, There are many other kinds of movements which are evidently 
independent of cells : for example, those of cilia and of spermato- 
zoids. The former are outside cells, and the latter only move when 
they are liberated from ceils. The contractile fibriliae of muscle are 
evidently not dependent for their inherent power on cells or other 
form of structure, but on the square-shaped molecules of which its 
substance is composed All these phenomena, therefore, are con- 
nected with the molecules themselves ; the force occasioning them is 
a molecular force, and has nothing to do with pre-existing cells, or 
supposed germinal centres, as some have imagined. 
Again, the power of combination between these molecules, which, 
under peculiar conditions, not only move, but so move as to advance 
towards and press upon each other, that they at length unite and 
produce higher forms, must also be attributed to a molecular force 
operating in obedience to fixed laws. Thus it was demonstrated by 
Newton, that in a sphere the total attraction resulting from the 
particular attraction of all its component parts, is, as regards any 
body drawn towards it, the same as if they had been concentrated 
at the centre. Hence minute spherical particles, as so many gravi- 
tating points, will be drawn towards each other with a force varying 
inversely as the squares of the distances between their respective 
centres. The author referred at length to the able descriptions of 
Mr Rainey,* as to the physical laws regulating the formation and 
disintegration of bodies by molecular attraction and repulsion as well 
as to the effects of molecular superposition, showing that the same 
* Op. cit. See also papers in the Microscopical Journal, i860. 
