Method of Regulation in Behavior and in Other Fields. \']'] 



green Paramoecium bursaria, in Euglena, and many other green 

 infusoria, light assists the metaboHc processes, while lack of light 

 interferes with them, and the same is true of the so-called purple 

 bacteria. All of these organisms react on coming to a region of 

 darkness by turning aw^ay and going elsew^here. In the colorless 

 Paramoecium caudatum and in the colorless bacteria ordinary 

 light does not affect the metabolic processes, so that there is no 

 interference with these processes in darkness, and we find that 

 they do not react on reaching a dark region, but enter it readily. 

 For all these organisms, colored and uncolored, light may be 

 made so intense that it does interfere with the physiological pro- 

 cesses, as is shown by the fact that the processes stop, the organ- 

 isms dying. To such light all react by turning away — including 

 even the colorless Paramoecium caudatum. We find in all of 

 these cases that the animal reacts by turning away when there is 

 interference with the physiological processes, and does not so 

 react unless there is such interference. 



In some cases the relation between behavior and the effect of 

 an agent on the physiological processes is marvelously precise. 

 Thus, Engelmann ('82) proved that in Bacterium (Chromatium) 

 photometricum the ultra red and the yellow-orange rays are those 

 which most favor metabolism (assimilation of carbon dioxid, 

 etc.). When a microspectrum is thrown on a preparation of 

 these bacteria, they are found to react in such a way as to collect 

 in precisely the ultra red and the yellow-orange. The reaction 

 consists in a change of behavior — a reversal of movement — at the 

 moment of passing from the ultra red or the yellow-orange to 

 other parts of the spectrum, while passing in the opposite direc- 

 tion produces no such effect. Bacteria are not in nature sub- 

 jected to spectral colors in bands, so that there has been no oppor- 

 tunity for the production of this correspondence between behavior 

 and favoring conditions through the selection of varying indi- 

 viduals. 



What is the explanation of these facts .f" Why does the infu- 

 sorian or the bacterium shrink back from darkness or the region 

 containing no oxygen.^ As a matter of fact, it requires the light 

 or the oxygen for the continuance of its metabolic processes, and 

 it does not shrink back from a region lacking them unless it does 

 need them. But we have no reason to attribute to the bacterium 

 any knowledge or idea of that relation. We do not need any 



