ECOLOGICAL FACTORS 417 



Some vertebrates seem to be negative to calcium. The fire sala- 

 mander (Salamandra salamandra) is absent in central Germany on lime 

 formations, but is numerous on sandstone, slate, red marl, and granite; 

 the larvae cannot develop in hard water. 141 



Soil containing common salt is peculiar in its flora and fauna. 

 It is characterized especially by a number of small beetles of the 

 families Carabidae, Anthicidae, and Staphylinidae, which occur in 

 widely separated regions, where corresponding conditions exist, and 

 are absent elsewhere. 142 Of the land snails, Helix pisana for example, 

 in southwestern Europe as far as southern England, and Pupa maritima 

 in Cuba, are limited to the seacoasts. In all these animals nothing is 

 known of their more intimate relations to the salt content of their 

 habitat. 



The herbivorous mammals, especially the ruminants, usually re- 

 quire sodium chloride; they use sodium to compensate for the large 

 amount of potassium which they secure from their plant food. 143 

 Hunters and fisher folk that live on an exclusively flesh diet may 

 dispense with salt, but not farm laborers who eat many vegetables. 

 Natural salt licks are eagerly sought by wild animals; the so-called 

 "bracks" in the southwestern African steppes are a gathering place for 

 the antelopes, which there satisfy their salt requirements toward the 

 end of the dry season. 144 For many species, a large supply of sodium 

 chloride is absolutely indispensable. According to Pallas, the Siberian 

 fat-tailed sheep degenerate when they are kept away from certain 

 salt meadows. The camel is dependent upon salt-containing plants; 

 it also eats greedily the white salty efflorescence on the ground of the 

 desert. The camel loses weight on the most fertile meadows if its 

 needed halophytes are not available. Where the salt licks and the 

 halophytes are absent in the mountains, wild camels are absent also. 145 

 Animals living in regions poor in iodine have the enlarged thyroid 

 glands known commonly as goiter. In some districts, such as the 

 region of the Great Lakes in North America, goiter is endemic, affect- 

 ing other animals as well as man. Animals living near the sea are 

 relatively free from goiter. Goiter can be experimentally controlled in 

 young animals by regulating the supply of iodine. 146 



Another peculiarity for which there is no satisfactory explanation 

 is the dependence of many animal groups upon the geological forma- 

 tions, a fact for which several statistical observations are at hand. 

 According to Gadow, 147 red sandstone is most favorable for amphibians 

 and reptiles on the Iberian peninsula; for amphibians, granite, Terti- 

 ary, Palaeozoic, and Mesozoic limestone become less favorable in the 

 order named; for reptiles, the Mesozoic limestone takes second place 



