ECONOMIC ZOOLOGY 501 



means of comrru'ive than the navigation of the sea. His 

 relatives in South America, the llamas, have long been used as 

 the chief animal of burden in the Andes. The reindeer is at 

 once camel, horse, and ox of the frigid zone. The dog is also 

 an efficient beast of burden over the snows. 



In modern times the horse has r-eme to be one of the most 

 valuable of animals used by man, .ranking in money value next 

 to the cattle in the United States. The mule, which is a hybrid 

 between the female horse and the male ass is a hardy, strong, 

 infertile animal and one of our most valuable beasts of burden 

 in agricultural communities. The student will not fail to 

 realize that more powerful groups of human beings have used 

 other men as animals in very much the manner we have been 

 describing. While slavery is not legalized over much of the 

 earth it is still known in other forms. 



Steam and electricity are replacing animal power at many 

 points, but there is little likelihood that it will entirely displace 

 them until population becomes so numerous that the animals 

 are more valuable as food than they can be as labor-saving 

 devices. 



504. Animals in Science and Medicine. A most inter- 

 esting way in which animals have been of value to the human 

 race grows out of the fact of the general likeness between man 

 and the lower animals. It is safe to say that the great ad- 

 vances in surgery which have accomplished so much in the 

 saving of human life have been made by early experimentation 

 on animals in the laboratory, even more than by the actual 

 direct study of the human body and its conditions. Experi- 

 ments quite impossible of being made on human beings have 

 first been tried on animals and have been found to accomplish 

 what was expected of them. But it is not merely in surgery 

 that they have shown themselves most valuable to human life. 

 In all the work on antitoxins and serums with which to combat 

 the germ diseases, the work must first be done on animals. 

 The antitoxin of diphtheria comes from the horse; the virus by 

 which we vaccinate for smallpox is obtained by giving the 

 disease to the ox, which is only mildly affected by it; and so on 



