£i' 



19 



lenc^tli of time. The periodicul emphasis of the lungs, 

 the lieart, the bowels, the uterus, and it may l)e also of 

 such l)usy laboratories as the livei-, tlie kidneys and the 

 stomacli, show tlie necessity of these periods of rest, 

 not to speak of intermittent sleep to the weary brain. 

 We can not think without p(;riods of rest of longer or 

 shorter duration. All careful experiments go to show 

 that any of these movements must be accompanied by 

 a corresi)on(Mn2r interchanoce between the external and 

 internal magnetic relations of muscular and nervous 

 fi])res, giving out heat and throwing off decomposed 

 matter during this activity. 



This partial reversal of sections of nerves and mus- 

 cles in their electrical relations is doubtless a normal 

 condition. Huxley in his "Lay Sermons" seems to 

 show this when explaining the circulation in a nettle 

 sting. lie says: 



The whole liair 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 iiiniimerable granules of extreme minuteness. This 

 semi-fluid, lining is protoplasm, wliich thus constitutes a kind of bag, 

 full of limpid liquid. When viewed with a sufiiciently high mag- 

 nifying power, the 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 

 waA'es. But in addition to these movements, and independently 

 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 di- 

 rections, and. thus there is a general stream up one side of 

 the hair and down the other. But this does not prevent the exist- 

 ence of partial currents which take difierent routes and sometimes 

 trains of granules may be seen coursing swiftly in opposite direc- 

 tions within a twenty thousandth of an inch of one another; which, 

 occasionally, opposite streams come into collision and, after a longer 

 or shorter struggle, one predominates. The cause of these currents 



