502 ZOOLOGY 



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. 



It has been discovered of late years that many organs of 

 the body secrete into the blood that passes through them, 

 certain substances that have a most important bearing on life. 

 Sometimes these organs become diseased and refuse to do their 

 work. This may be true of the digestive glands, of the thyroid 

 glands in the neck, and others. In such cases the gastric juice 

 of the pig, or the thyro-iodin obtained from the thyroid of the 

 sheep, or pancreatin obtained from other animals may be ad- 

 ministered in such a way as to carry on the function or even to 

 overcome the disease. 



Frogs, rabbits, guinea-pigs, cats, dogs, sheep, cows, horses, 

 and monkeys are among the animals that have been most 

 useful in these respects. 



505. Miscellaneous Uses of Animals. A long list of minor 

 and exceptional uses of animals could be mentioned. The dog 

 and cats have some protective value about the homes of men, 

 where they were long before recorded history began. They have 

 kept homes free' of vermin, as rats and mice and the smaller 

 animals, and the dog has doubtless been of protection from 

 other enemies. They have been companions for childhood 

 through all history. 



The skins and tendons and bone of animals figured largely 

 in all the early home industries, as sewing and tying and the 

 like. In modern times the skins are used in many ways, as rugs 

 and home ornaments, in the making of bags and other receptacles. 

 Horn, bone, and ivory from the teeth and tusks of animals are 

 largely used in knife handles, piano keys, billiard balls, and 

 numerous other objects. Whale oil (sperm oil) has long been 

 used in making candles, though it has now been supplanted 

 by the cheaper mineral oils. Bristles, brushes, perfumes, oils, 

 glue, buttons, and fertilizers are only a portion of the numerous 

 by-products of the modern meat-packing houses. Ornaments 

 are made of teeth, of corals, and of pearls. Many animals are 



