392 
PHYSIOLOGY. 
BOOK II. 
lip any coloured fluid, or, at least, not till they receive it in an 
altered state from other forms of tissue. 
Corti, in 1774, Fontana, L. C. Treviranus, and especially 
Amici, made the earliest observations upon rotation. It was 
found that if a portion of Nitella flexilis, or even of the crusta- 
ceous Charas, their opake cuticle being first scraped away, 
be examined, a current of sap will be distinctly seen in each 
cellule, setting from joint to joint, flowing down one side and 
returning up the other, without any membrane intervening to 
separate the opposing currents ; each cellule has a movement 
of its own, independent of that of the cellules above and below 
it ; sometimes the movement stops, and then goes on again 
after a brief interval ; if a cellule is divided into two by a 
ligature passed round it, a separate movement is seen in each 
of the divisions ; this motion is rendered distinctly obvious by 
the numerous minute green granules which float in the trans- 
parent fluid, and which follow the course of the currents. 
The observations of Amici have been verified and much 
extended by subsequent investigations. 
Among other things, it has been ascertained that in Nitella 
the currents have alw^ays a certain relation to the axis of 
growth, the ascending current uniformly passing along the 
side of the cell most remote from the axis, and the descending 
current along the side next the axis. 
Mr. Varley considers (Trans. Soc. Arts, xlix. p. 20.) that, 
in addition to the principal current, which he finds setting 
up one side and down the other within the green interior 
granular sac of each joint of Chara, there are two others, of 
which one takes place between the side of the interior sac 
and the side of the outer transparent coating, the other 
current is said to occur in the centre of the interior cell, and 
to be very sluggish. 
A further and very detailed examination of the Chara 
fragilis has been made by M. Dutrochet, the general results 
of which are to be found in the Ann. des Sciences, n. s., vol. ix. 
p. 73. It appears from theni, among other things, that ex- 
periments, expressly instituted by M. Becquerel, show the 
motion notio be owing to a voltaic action of the green globules 
lining the cells, nor to any known form of electrical agency. 
