Effects of Light and Heat on Organisms. 417 



ment will continue for a time through previously established habit, 

 which is the momentum of former impulses, but will soon become erratic 

 and in time cease. People living in dark places are unhealthy and their 

 children are apt to be deformed. ' ' Some poor people having taken up 

 their abode in the cells under the fortifications of Lisle, the proportion 

 of defective infants produced by them became so great that it was 

 deemed necessary to issue an order commanding these cells to be shut up. " 

 (Robert Chambers. ) In the absence of light, if other conditions are 

 favorable, tadpoles will continue to grow indefinitely as tadpoles, but 

 will never undergo their normal metamorphoses into frogs. If they are 

 exposed to the action of green light alone they cannot undergo their 

 metamorphoses. Their legs and lungs will not develop, their gills are 

 retained, and after awhile they die. Green light is the same as dark- 

 ness to them. It is said that the young of the medusae (jelly fish ) if 

 confined in the dark will continue to form others by budding, thus re- 

 maining only polyps, and will go on in their development to perfect me- 

 dusae, only when properly exposed to light. The eggs of frogs will not 

 develop in the dark. Those hatched under dark paper are abortions and 

 rudimentary. Certain infusoria act under the influence of light in the 

 same way that the chlorophyl zoospores do, moving into its influence 

 from a shade. 



Light directly affects both the temporary and permanent color of the 

 different races of men, the habitual effects finally becoming hereditary 

 and permanent. Many of the same race have been entirely differentiated 

 from each other in color. Some of the Hindoos of the north are white, 

 while those of the Deccan are black. The Jews, scattered through all 

 countries have almost as many shades of color, from the fair white of 

 the north of Europe to the black of Tunis. The Tuariks of Mt. Atlas 

 are of a light brown, while those south of the great desert are black. 

 The Esquimaux are whiter in winter than in summer. " It is believed 

 that under certain circumstances fair races may become dark, and dark 

 races light, the cuticle, however, being affected sooner than the hair or 

 the iris of the eyes. In the southern, as in the northern, hemisphere, we 

 we find a zone of lighter colored people running through the temperate 

 regions. The Caffres of South Africa are not so black as the negroes 

 of the tropics, and in South America the Patagonians and the Fuegians 

 are lighter in tint and taller in stature than the races nearer the Equator. 

 Some of the Araucanians of Chili are almost white The physical 

 strength and great stature which distinguish the Northern Europeans 

 are reproduced under similar conditions of climate among the Patagon- 

 ians." 1 



It cannot be said that the differentiation of pigments in the animal 

 1 Taylor's Origin of the Aryans, 100. 



