THE VITAL PHENOMENA OF CELLS 45 



In most cases ciliary movement is not influenced in any manner by the 

 adjacent or by the distant cells, and in the mucous membranes of the vertebrates 

 it appears to be entirely independent of nerves; for ciliated cells continue to 

 move after they are cut out of the body, and in the human body for as much 

 as three days after death (Valentin). Hence it is the more remarkable that in 

 a row of cells the cilia always move in complete harmony even if the cilia are 

 not in contact with each other. This and the further fact that a stimulus, 

 applied to a portion of the epithelium where ciliary motion has ceased, can be 

 transmitted to a portion where it is still active, go to show that the basal part 

 of the cell must have something to do with the regulation of ciliary movements. 

 Nevertheless much here remains to be explained. 



5. Still other forms of movement than those already discussed occur in 

 the animate world. The following may be briefly mentioned. Various uni- 

 cellular animals (Radiolaria, Rhizopoda) can raise or lower themselves in the 

 water where they live by changes in their specific gravity. Arcellae and Diffhi- 

 giae rise by developing a bubble of carbon dioxide in their cell body. Thalassi- 

 cola (Fig. 15) swims at the surface of the sea because its vacuoles contain a 

 fluid specifically lighter than sea water. Under certain conditions it can sink 

 itself by rupturing the sheaths of the vacuoles which then fuse together. When 

 the vacuoles are reformed the animalcule once more mounts upward. Finally, 

 in plants a great many movements occur through swelling of the cell wall,, 

 and through changes of turgor, which we cannot discuss in this book. 



H. PRODUCTION OF LIGHT 



Certain putrefactive Bacteria which live on decaying flesh of marine 

 fishes and on meat, as well as certain Fungi and a few insects have the power 

 of producing light. In certain places where the sea water glows it is found 

 on filtration that the glowing substance remains on the filter and is not found 

 in the filtrate; the cause of the light is therefore an insoluble substance. 

 Microscopical examination of the residue on the filter reveals millions of 

 phosphorescent organisms belonging to all classes of the invertebrates. 



That the phosphorescence of these animals is not due to previous exposure 

 to the sun's rays follows from the fact that even when they are kept for a long 

 time in complete darkness, they glow just as strongly as their companions which 

 have been in the sunlight. The phosphorescence ceases however when the ani- 

 mals are brought into a medium unsuitable for respiration; it therefore repre- 

 sents a true oxidation process. 



Closer investigation of this phenomenon proves that it is initiated by the 

 activity of the living protoplasm, for the organisms produce light only so long 

 as they are alive. In the case of Pholas (a mussel), the phosphorescent sub- 

 stance can be thrown out of the body, but it is formed only by the- activity 

 of the living protoplasm. The phosphorescence arises through the action 

 of a special enzyme on this substance (R. Dubois). In the "lightning bug," 

 Lampyris, nerve fibers have been demonstrated running to the light-producing 

 organ. The animal suppresses its light when there is a noise; the darken- 

 ing then begins at the proximal end and spreads to the distal end of the 



