832 THE AMERICAN NATURALIST. [Vou. XXXIIl. 
PSYCHOLOGY. 
Psychology of Paramecium. — The analysis of the reactions of 
Paramecium from a psychological standpoint has been undertaken 
by H. S. Jennings.’ It is well known that Paramecia will swarm in 
great numbers around masses of food. It is also well known that 
they form large shoals after having been dispersed in a fluid, and 
that they avoid centers of alkaline reaction and frequent regions 
showing acid qualities. Such reactions as these have led many 
investigators to conclude that Paramecium has sensations, exerts 
choice, possesses social instincts, and, in fact, exhibits in an ele- 
mentary way all the essential characteristics of an intelligent animal. 
Dr. Jennings’s work has shown that Paramecia take up any foreign 
particles irrespective of their appropriateness as food, and, further, 
that these organisms will collect around a piece of inert filter paper 
with as much avidity as around a mass of real food. This is due to 
the fact that the normal forward motion of the infusorian is suspended 
the moment the animal comes in contact with a solid body, and the 
animal lies slowly rotating next the body with which it is in contact. 
Most solid bodies then become centers around which Paramecia 
accumulate. The social instinct of forming shoals is shown to be 
due to the influence of carbon dioxide. When for any reason two 
or three Paramecia stop together, the amount of carbon dioxide pro- 
duced seems to be sufficient to ensnare and hold others, and thus the 
nucleus of a shoal is formed. The large assemblies of Paramecia are 
held together, not by social instinct, but by their own carbon dioxide. 
The so-called attraction for carbon dioxide and other acids is shown 
not to be an attraction. The organisms running at random pass 
eventually into an acid region, at the edges of which they always 
react in such a way as to remain within the acid area. In a 
similar way there is no repulsion from alkalis, but when met the 
animal ‘reacts by turning aside. In this way the reactions of 
Paramecium are reduced to simple machine-like responses, which 
no more require the assumption of intelligence for their performance 
than does the contraction of an isolated muscle. bur 
1 Jennings, H. S. The Psychology of a Protozoan, American Journal of 
Psychology, vol. x, no. 4. 
