No. 400.] REACTIONS OF INFUSORIA TO CHEMICALS. 263 
The essential feature of the characteristic motor reaction of 
these organisms, as I have described it, is that they turn, when 
they do turn, toward a structurally defined. side, whatever the 
line of action of the stimulus. For example, the organism in 
the figure (one of the Hypotricha) turns to the right, in the 
direction indicated by the curve c-Z. But evidently the organ- 
ism may come into the position 4— as easily by turning to the 
right as by turning to the left; in the former case it must 
simply keep turning somewhat longer. As a matter of fact, 
orientation to most stimuli occurs in the Hypotricha in exactly 
the manner illustrated — by turning to the right. This is true 
for chemical, osmotic, mechanical, and thermal stimuli ; whether 
for electric stimuli and light has not been shown. 
The precision of the orientation, and whether a large number 
of organisms will be oriented in the same way, depends upon 
the question as to what influences produce the motor reaction. 
Suppose that in the figure the stimulating agent is something 
that acts steadily in lines coming in the direction of the 
straight arrows. Now, I have shown in the Fifth of my 
Studies that many of these organisms are much more sensi- 
tive at the anterior end than elsewhere, so that a stimulus at 
the anterior end produces a different effect from a stimulus 
elsewhere on the body. When, therefore, the organism is so 
oriented that the lines of force impinge directly on the anterior 
end (position 4—0), it will, of course, be differently affected as 
compared with a position in which the sensitive anterior end is 
wholly or partly protected by the remainder of the body. Thus 
different reactions may be caused in the two cases; in one 
position the motor reflex may be caused, in the other not. If, 
for example, the motor reflex is caused when the lines of force 
impinge on even a small part of the anterior end, then the 
organism will not cease giving the reaction until it is oriented 
with anterior end directed away from the side of incoming 
which Garrey makes for my information, I had already developed at length to 
show their.identity in character, in two papers (Amer. Journ. of Phys., vol. ii, p. 
339; Amer. Journ. of Psychol., vol. x, p. 513). I had counted it a chief result of 
my work that it had reduced the supposed attractions and repulsions of these 
organisms to a motor reflex “ of the same order as the motor reflexes of higher 
animals," as I have expressed it elsewhere. 
