^SS.KTi86?] PKOGBESS or MICROSCOPICAL SCIENCE. 113 
results : — The course of the phenomena following the irritation of a 
single interrupted discharge from the coil is, says the author, deter- 
mined by the intensity of the current and the condition of the proto- 
plasm previous to the excitation. When the Amoeba is acted on by 
the current, it is seen — when the animal has an elongated form, and 
moves with a regular velocity (0-01 to 0*2 mm. per second) — that the 
following events occur. A. In Case of Feeble Irritation. — After a 
short period of latent action, or even very rapidly, there is a sudden 
slackening or suspension of movement on the part of the granulations 
of the protoplasm, without any appreciable change of form on the 
part of the animal. In a few seconds more there is a gradual re- 
establishment of the current, and of the displacement of the granu- 
lations in the primary direction, without change of form on the part 
of the animal. Total duration of action, five seconds, maximum. 
B. In Case of a Medium Degree of Irritation. — Period of latent action 
hardly perceptible. Immediate arrest of granulations without change 
of form on part of animal. In about three seconds more there is a 
change of form (contraction) on the part of the animal, consisting in 
shortening and thickening of the Amoeba (assumption of spherical 
form). During these changes the anterior part of the animal remains 
fixed by adhesion to the glass. The assumption of the spherical form 
is the more complete and rapid as the current is stronger. The time 
of contraction in case of feeble irritation may be about two seconds. 
The maximum of shortening may last for some time. Moreover, when 
the irritation has been very feeble, the granulations immediately 
recommence their circulation, and produce lateral expansions of the 
protoplasm. One of these expansions progressively increases, till it 
absorbs the total mass of the protoplasm, which thus being restored to 
the primitive elongated form, begins to move with regularity. The 
total duration of action is from about ten to fifteen seconds. C. In 
Case of a Powerful Irritation. — Here there is immediate arrest of the 
course of the granulations and commencement of contraction, which in 
about two seconds produces the maximum degree of shortening, that is to 
say, the more or less complete spherical form. After from half a minute 
to a minute and a half there is a re-establishment of the movement of 
the granulations, and formation of lateral expansions. In about two 
minutes the original condition of things is restored. When the 
Amoebae experimented on are large and flat, and provided with short 
expansions, the effect of irritation differs according as a single shock 
or a series of shocks is given. The first action still consists in an 
arrest of the movement of the granulations, and of a very slight con- 
traction. Soon after the Amoeba becomes elongated nearly to a 
cylinder, and moves very rapidly in one direction, almost without 
change of form. Meanwhile, if the irritation is renewed, there is 
again an arrest of the granulations, and contraction takes place. The 
phenomena exhibited by Arcella vulgaris under the influence of 
electricity are, says M. Engelmann, best seen when the animal 
encloses a number of air-bubbles at the moment of excitation. The 
specimens best suited for observations of this kind are those which 
swim at the surface of a drop of water, the dorsal surface being next 
VOL. II. I 
