Decomposition and Regeneration 297 



by snails, mammals, and certain other land animals. As mentioned in 

 Chapter 3, especially fine race horses are raised in the bluegrass region 

 of Kentucky. Here the abundance of calcium and phosphorus in the 

 grass makes possible the healthy bone growth of the young horses. 

 The fire salamander is an example of an animal that avoids calcium 

 soils. The special need of aquatic organisms for lime has been dis- 

 cussed in the previous chapter. 



Certain elements and vitamins are required by animals in only 

 trace quantities, but, if these minute amounts are not present in the 

 diet, serious deficiency diseases and eventually death result. In re- 

 gions such as the belt from Washington east to Montana and south 

 to Colorado, in which iodine is deficient in the soil, the plants, al- 

 though themselves healthy, do not contain the amount of iodine 

 needed by animals feeding upon them. As a result goiter develops 

 in live stock, and also in human consumers, unless extra iodine in 

 the form of iodized salt is added to the diet. 



Zinc, iron, copper, and cobalt are other elements needed in trace 

 amounts by animals. Zinc is essential in one of the enzymes involved 

 in respiration, and the other three elements mentioned are concerned 

 with formation of hemoglobin, tlie deficiency of which produces 

 anemia. In certain parts of Scotland and of Australia all attempts 

 at sheep raising were unsuccessful until the difficulty was finally 

 traced to the lack of cobalt in the soil. Only very small amounts of 

 cobalt given the sheep directly, or applied to the grazing areas as 

 fertilizer, were needed to bring about a remarkable improvement in 

 the growth of the animals. 



The similar need of animals for vitamins obtained from the food is 

 too well known to require extended comment here. Only minute 

 quantities of vitamins are consumed, but these are absolutely neces- 

 sary and must be obtained directly from the plants that manufacture 

 them or in some other way, if the animals are to survive. Control of 

 the lives of animals and of other heterotrophic forms by the nutrient 

 factor may thus involve the sufficiency in amount of the common food 

 stuffs, the availability of essential accessory substances in extremely 

 small quantities, or some other necessary aspect of nutrition. 



DECOMPOSITION AND REGENERATION 



Since the food of animals and of other heterotrophic forms is de- 

 rived from green plants or from the bodies of organisms that are di- 

 rectly or indirectly dependent upon green plants, the nutrition of 

 these phototrophic forms is clearly of basic importance in the natural 



