4OO ELEMENTARY ZOOLOGY. 



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 

 cummunities. 



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. 



400. 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 advances in surgery which have accom- 

 plished so much in the saving of human life have been 

 made by early experimentation on animals in the labora- 

 tory, quite as much as by the actual direct study of the 

 human body and its conditions. Experiments quite im- 

 possible of being made on human beings have first been 

 tried on animals and have been found to accomplish 

 what w r as 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 w r e vaccinate 

 for small-pox is obtained by giving the disease to the ox, 

 which is only mildly affected by it; and so on through a 

 considerable list of such diseases. The most hopeful 

 work that is now being done to give us control of the 

 terrible disease of cancer is being done on mice and rats, 

 otherwise an enemy to human interests. 



