370 



GENERAL PHYSIOLOGY 



manner on the inner surface of the vessel. From these 

 experiments it is very clear that oxygen acts as a stimulus, giving 

 rise to the expansory phase of protoplasmic movement. 



The production of other forms of energy besides that of movement 

 is also excited by chemical stimuli. Since it would, however, lead too 

 far to consider all the excitation-effects of such stimuli, only the 

 facts connected with the production of light will be presented. 



FIG. 161. Chemical stimulation of the sartorius muscle. of the frog. 



For the investigation of this the unicellular organisms are best 

 fitted, for in them all conditions are simplest and most easily 

 observed. It is known of many unicellular organisms, Bacteria, 

 Radiolaria, etc., that they develop light as the result of chemical, 

 as of various other stimuli. But light-production has been 

 investigated most frequently and in most detail in the Noctilucce, 



the peculiar Flagellata which usually 

 produce the light on the surface or 

 the water in our northern seas (Fig. 

 163). Recently Massart ('93) has 

 studied again in detail the action 

 of chemical stimuli upon them. In a 

 vessel containing sea-water, in which 

 the Noctilucce rested quietly upon the 

 surface without emitting light, he 

 placed carefully with a pipette various 

 substances, such as distilled water, a 

 concentrated solution of common salt, 

 a solution of sugar, etc., and in each 

 case let the drop spread slowly over the 



surface of the sea- water. The result was that as soon as the liquids 

 introduced came into contact with the Noctilucce, the latter became 

 brilliantly lighted, and the pleasing spectacle was presented of a 

 slowly widening, glowing circle, spreading over the surface of the 

 water. A similar phenomenon can be observed very well in 

 Radiolaria, especially in the large Thalassicolla, which emits light 

 actively upon a change in the concentration of the sea-water in 



FIG. 162. Production of rhythmic con- 

 tractions in the sartorius muscle 

 by chemical stimulation. 



