974 The American Naturalist. [ November, 
General Notes. 
GENERAL BIOLOGY. 
Reactions to Stimuli in Paramecium.'—The plan of the au- 
thor has been to study the reactions of one organism so completely and 
exactly that we may gain a good idea of its daily activities. Phenom- 
ena such as these are to be explained. When a large number of Para- 
mecia are transferred, together with a bit of decaying vegetable mat- 
ter, from the culture jar to the glass slide and covered with a properly 
supported cover-glass, we see the Paramecia at first uniformly dis- 
tributed, a few minutes later beginning to gather about the decaying 
particle, and soon all accumulated there. Some minutes later the Para- 
mecia begin to disperse, but are always sharply confined within an 
ever extending circumference. If an electric current is now passed 
through the water, the infusoria swim towards the cathode, but do not. 
pass the circumference. We seek an explanation of the aggregation 
of the infusoria, their subsequent dispersion and their limitation by an 
invisible boundary, even when urged to pass it by the electric current. 
The results of a series of experiments which cleared up one difficulty 
after another in a manner very interestingly described are as follows: 
The beginning of the accumulation of the Paramecia is due to thigmo- 
taxis. An individual, hitting the solid body by chance, stops, perhaps 
starts back and whirls on its axis, then settles against the object and 
remains there. Others do likewise; thus the accumulation begins. 
No response occurs to smooth hard bodies. The close application of 
the Paramecium to the surface and the gliding over it are the results 
of the peculiar reactions of the cilia induced by the stimulus. But the 
rapid and complete aggregation cannot be accounted for alone on the 
ground of thigmotaxis. The author finds that Paramecia are attracted 
by a not too strong concentration of carbon dioxide. The CO, produced 
by the thigmotactic individuals serves to lure the others. But after the 
crowd has become very dense the CO, becomes so strong in their vicin- 
ity that the Paramecia are repelled from the region of the solid body _ 
and begin to disperse. They do not scatter widely into the culture 
1 H, S. Jennings. Studies on Reactions to Stimuli in Unicellular Organisms. 
I. Reactions to Chemical, Osmotic and Mechanical Stimuli in the Ciliate Infu~ 
soria. Jour. of Physiology, X XI, p. 258-332, May, 1897. 
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