DIET OF ANIMALS. 199 



seek salt, and congregate at certain periods of the day at points where 

 salt is to be found, and will eat earth when sodium chloride is not to be 

 obtained. This, as already mentioned, is to be explained by the fact that 

 vegetable matters are poor in sodium salts and rich in potassium salts. 

 So, also, the granivorous birds will devour gravel, stones, and sand from 

 an instinct which leads to their taking such substances into their gizzard 

 to enable them to properly triturate their food ; for, in the granivorous 

 birds, the nutritive principles of the seeds are inclosed within dense mem- 

 branes. They are not provided with teeth for the mastication of food, 

 and, were no means supplied for crushing or triturating their food, 

 would starve to death with their stomachs full of the most nutritious 

 seeds. 



The diet most in harmony with the organism, teeth, alimentary 

 canal, etc., of animals may be modified if the force required of animals 

 is increased artificially. Thus, the horse in a state of nature is never 

 granivorous or fructivorous, but only eats herbs ; when in the service of 

 man grains are necessary to reduce the bulk of food, for horses cannot 

 work if their stomach or alimentary canal is distended with forage. By 

 the administration of oats the duration of the feeding time and of the 

 period of digestion is reduced. There is economy of the digestive secre- 

 tions, the stomach is much less distended, and there is less time required 

 for digestion ; hence, herbivorous animals in domestication become 

 largely granivorous, and oats form a large portion of their food, for oats 

 are always nutritious in small bulk and readily digested. They eontain 

 all the food-elements in suitable proportions ; the large amount of nitro- 

 gen which they contain render them particularly suitable for repairing 

 waste in the muscular system, especially when work is demanded of them. 

 Oats nourish, therefore, without fattening. Since the process of diges- 

 tion in the herbivora and carnivora, and the ultimate nature of their 

 food-stuffs is identical, it is natural to suppose that their nutritive habits 

 may be changed ; thus, the herbivora may be brought to feed on animal 

 matter, while the carnivora may be led to feed on matters of purely vege- 

 table origin. Numerous facts of this kind have been over and over 

 again reported. The most striking of all is seen in the results of the 

 domestication of the common cat. Here a typical carnivorous animal 

 by education and habit becomes almost herbivorous. So, also, pigeons 

 have been accustomed to eat meat to such a point that they will after- 

 ward refuse seeds. In Iceland, where vegetation is sparse, the native 

 horses arid oxen have been seen to feed upon fish, and it is even stated 

 that they have been seen to enter the water and fish for themselves. The 

 starting point of this change from the herbivorous into the carnivorous 

 t} r pe is found in the fact that all animals after their birth are carnivo- 

 rous ; for in suckling animals there is but little if any difference in their 



