4 NERVOUS SYSTEM AND SENSE-ORGANS 
studying a very simple organism, such as the Proteus Animal- 
cule (Ameéa), which is a particle of comparatively pure proto- 
if 
plasm (fig. 1006). That this creature is sensitive to mechanical 
stimuli is easily proved by tapping the glass slide on which one 
of the body (pseudopods) by which creeping is effected will be 
drawn in, and the animal will assume a spherical form (fig. 1006, 4). 
A good example of chemical stimu- 
A 
1 (8) very weak caustic potash to the 
species of Amceba (4. max) is 
B moving along, the reaction consisting 
in this case of the protrusion of long 
pointed pseudopods (fig. 1006, 8B). 
The same kind of Amceba reacts in 
a marked way to changes of tem- 
perature (fig. 1006, c). At freezing 
C 
x o° C. to 35°C. it moves about with 
\ ever-increasing activity; above this 
40 
and at about 4o’C. the animal has 
25 assumed a spherical form, and dies 
>? )* in a condition of ‘“heat-stiffening ” 
<—— or coagulation. This illustrates very 
Fig. 1006. — Proteus Animalcules (Amada), 
oe eee eres stimulus has only a certain range of 
action, the range in this case being 
between oC. and 40°C., which are known as the smznzmum 
Between these two points is an optimum one (35° C. in this 
instance), at which the stimulus exerts its greatest effect by 
way of promoting activity. Light does not appear to affect 
taking in of food, which process goes on most actively at night. 
If a constant current of electricity is passed through the body 
of an Amceba which is protruding pseudopods in all directions 
is crawling about under the microscope. The protruding lobes 
lation is afforded by the addition of 
@0O 
water in which the slug-shaped 
| : 
point (0° C.) it is spherical and inert; 
as the temperature increases from 
1 
a ae the activity gradually diminishes; 
D 
Boe 
much enlarged, showing effect of various stimuli. well the fact that any particular 
and maximum points of heat-stimulation for this particular animal. 
the creeping movements of Ameceba, but is said to check the 
it will begin to creep against the current, and all those pseudo- 
