940 Transactions of the American Institute. 



ou a dark ground, or is lighted from beneath through a diaphragm. 

 Further researches proved that it is not the intensity but the 

 direction of the rays of light, which governs the movements of 

 microscopical organisms. From a great number of experiments, 

 Prof. Cohn draws conclusions which may be thus abbreviated: 



1. The direction of the movements of green organisms is deter- 

 mined by the direction of the rays of light which fall upon them. 

 They are attracted rectilinearly by the source of light. Apparent 

 exceptions to this rule are brought about simply by the form of 

 the drop or mass of water containing them. 



2. They exhibit a polar relation to light; the celia (which is 

 called the head) and that part containing no chlorophyl is turned 

 toward the light, and the green portion away from it. 



3. All movements are accompanied by a rotation of their bodies 

 around a longitudinal axis passing through the head and tail. 

 While in the dark they can turn from right to left, or left to right, 

 but under light they have a definite direction which is contrary, in 

 euglense, to the hands of a watch, and the same as the rotation of 

 the earth. 



4. Experiments with colored glass show that only the more 

 refrangible or actinic rays induce this direction. The organisms 

 are more strongly attracted by the blue rays, while the red are the 

 same as total darkness. If one-half of tke ield is lighted by blue, 

 and the other by red, they will go to the blue side, even if it be 

 turned away from the window edge. There are some exceptional 

 forms which turn away from the source of light by a backward 

 motion, and afterward return to it. 



5. It appears probable that all these phenomena, as far as direc- 

 tion of movement is concerned, depend upon the chemical activity 

 of these bodies. We can, in fact, imitate many of these move- 

 ments by purely chemical processes, with the help of what may be 

 called artificial euglena, viz: a fusiform fragment of chalk, having 

 one-half covered with a resinous cement, which, when placed in 

 diluted sulphuric acid, develops chemical action in its uncovered 

 half, and by the backward impulse thus generated in the direction 

 of the covered end, the chalk is made to rotate. 



ELECTROLOSIS OF TARTARIC ACID. 



M. Bourgoin's Memoir, brought before the French Academy of 

 Sciences, gives his researches on the action of the electric current; 

 first, ou neutral tartrate of potash; second, on a mixture of neutral 



