Ill ON THE PHYSICAL BASIS OF LIFE 135 



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 semifluid matter, full of in- 

 numerable granules of extreme minuteness. This 

 semi-fluid lining is protoplasm, which thus con- 

 stitutes 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 

 sufficiently high magnifying power, the proto- 

 plasmic layer of the nettle hair is seen to be in a 

 condition of unceasing activity. Local contrac- 

 tions 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 successive 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 cur- 

 rents in adjacent parts of the protoplasm take 

 similar directions ; 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 some- 



