398 
PHYSIOLOGY. 
BOOK II. 
renewal of motion when it has stopped : to light; because that 
agent determines the direction of growth: to contraction^ which 
is the effect of irritability ; not however, a contraction with 
successive pulsations, as in arteries, but by a simultaneous 
action throughout the whole length of the vessel, whose latex 
is thus brought into a state of powerful tension. Con- 
traction, however, cannot be the first cause of the motion, 
for it is not even sufficient to change the direction of the 
currents. When a vessel has been cut through at both ends, 
it has discharged all its contents by that end to which the 
current had been directed, and not by the other. But these 
are to be regarded as secondary causes only ; the essential 
cause is the perpetual oscillation of the globules. They have 
an incessant tendency to unite and to separate, without the 
one tendency ever overcoming the other ; and, as the organic 
(molecules) elements of vessels are of the same nature as 
the globules of latex, it follows that the walls of the vessels, 
and the globules they contain, have the same tendency to 
approach and retreat, as the globules themselves have with 
respect to each other. As this motion of coming and going 
takes place in a determinate direction, it necessitates and 
regulates the progressive motion of the latex. This law, 
says M. Schultz, is, for the physiologist, what attraction and 
repulsion are for the investigator of physical actions; it is 
final, and explains phenomena because it is itself placed 
beyond the reach of explanation. [This opinion is strongly 
objected to by the committee who reported upon M. Schultz’s 
paper.] 
7. Cyclosis is analogous to the motion of the blood in the 
lower animals, such as Nephelis vulgaris, Planarias, Nais 
proboscidea, and Diplozoon paradoxum ; or in the foetus of a 
fowl, before the heart is formed, when, as Malpighi and 
Wolff have shown, the blood moves spontaneously in the vas- 
cular apparatus. Nevertheless, although there is in plants 
no heart, or centre of circulation, it appears that there 
are certain foci, concerning which M. Schultz speaks thus 
(Comptes rendus^ vi. 583.) : — In Commelina coelestis there is 
a bundle of laticiferous vessels, which are very delicate and 
filamentous, compact and united in the form of a net with 
