282 THE Microscope. 
exquisitely delicate hairs, which cover its surface. Each sting- 
ing needle tapers from a broad base to a slender summit, which 
though rounded at the end, is of such microscopic fineness that 
it readily penetrates and breaks off in the skin. The whole hair 
consists of a very delicate outer case of wood, closely applied to 
the inner surface of which is a layer of semi-fluid matter, full of 
innumerable granules of extreme minuteness. This semi-fluid- 
lining is protoplasm, which thus constitutes a kind of bag, full 
of a limpid liquid, and roughly corresponding in form with the 
interior of the hair which it fills. When viewed with a suffi- 
ciently high magnifying power, this protoplasmic layer of the 
nettle hair is seen to be in a condition of unceasing activity. 
Local contractions of the whole thickness of its substance pass 
slowly and gradually from point to point, and give rise to the 
appearance of progressive waves, just as the bending of success- 
ive stalks of corn by a breeze produces the apparent billows of 
a corn field. But, in addition to these movements, and inde- 
pendently of them, the granules are driven, in relatively rapid 
streams, through channels in the protoplasm which seem to have 
a considerable amount of persistence. Most commonly, the 
currents in adjacent parts of the protoplasm take similar direc- 
tions; and thus there is a general stream up one side of the hair 
and down the other. But this does not prevent the existence of 
partial currents which take different routes; and sometimes 
trains of granules may be seen coursing swiftly in opposite di- 
rections, within a twenty-thousandth of an inch of one another; 
while occasionally opposite streams come into direct collision, - 
and after a longer or a shorter struggle, one predominates. The 
cause of these currents seems to. lie in contractions of the proto- 
plasm which bounds the channels in which they flow, but which 
are so minute that the best microscopes show only their effects, 
and not themselves. | 
The spectacle afforded by the wonderful energies prisoned 
within the compass of the microscopic hair of a plant, which we 
commonly regard as a merely passive organism, is not easily for- 
gotten by one who has watched its display continued hour after 
hour, without pause or sign of weakening. The possible com- 
plexity of many other organic forms, seemingly as simple as the 
protoplasm of the nettle, dawns upon one; and the comparison 
of such a protoplasm to a body with an internal circulation, 
