ECONOMIC ZOOLOGY. 401 



It has been discovered of late years that many organs 

 of the body secrete into the blood that passes through 

 them, or elsewhere, 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 thyroidin obtained from the thyroid of 

 the sheep, or pancreatin obtained from other animals 

 may be administered 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. 



401. Miscellaneous Uses of Animals. A long list of 

 minor and exceptional uses of animals could be men- 

 tioned. 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 ene- 

 mies. 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 been supplanted by the 

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