PHOSPHORESCENCE 1 35 



die. Thus the malarial organism which infests the red cor- 

 puscles of man passes through its life-cycle in two or three 

 days according to the species. The moment when it bursts 

 out from the red blood corpuscle is the time when tlic malarial 

 patient suffers his highest fever, and this occurs rhythmically 

 every two or three days. 



Many of the pigment cells which occur in animals are 

 rhythmic. They are influenced by hght and darkness, day 

 and night. The pigment-cells of the chameleon-shrimp, 

 Hippolyte, by contracting and expanding are able to vary the 

 colour of the crustacean so that it resembles its surroundings. 

 Whatever the colour of the background is, that will be the 

 colour of the shrimp during daylight. But as night comes on 

 these cells arrange themselves in such a fashion that the shrimp 

 becomes a light, somewhat Cambridge blue all over, no matter 

 what is the colour of its background. These pigment-cells ex- 

 hibit a daily periodicity corresponding with light and darkness. 



Similarly the organisms which cause the phosphorescence 

 of the sea react only when it is dark. During the day 

 they show no hght, but if disturbed during the night they 

 emit flashes of phosphorescence which can be readily seen from 

 the bows of a steamer or when the oars of a boat beat the water. 

 Samuel Pepys mentions this phenomenon in his Diary. He 

 noticed "the strange nature of the sea- water in a dark night, 

 that it seemed like a fire upon every stroke of the oar." One 

 of the chief causes of the luminosity of the sea is a unicellular 

 protozoon known as Noctiluca. Like the pillar of cloud which 

 led the Israelites, it becomes bright by night and dull by day. 

 If you capture some of these little creatures and keep them 

 in an aquarium in a photographer's dark room you would see 

 that they became phosphorescent after night-fall, even though 

 there were no change in the illumination of the dark chamber. 

 These animals seem to remember the time to glow and the 

 time to remain dull in their original more natural surroundings. 



Rhythm is often very well marked in cell-division. In the 

 developing eggs of certain animals the various cells divide 

 at almost exactly the same instant for the first six or se\en 

 divisions. This results in the formation of a perfectly 

 symmetrical hollow ball of cells. 



