186 STUDIES IN PHYSIOLOGY 



fully followed : (1) the sprained member should be placed 

 at once into cold water or into hot water and held there for 

 some time ; (2) it should meanwhile be rubbed as vigorously 

 as possible without causing pain ; (3) arnica, Pond's extract, 

 or some other " pain killer " should be applied ; (4) the 

 sprain should then be bound in a tight bandage (these four 

 applications tend to keep down the swelling) ; and (5) (most 

 important of all) the joint should have complete rest until all 

 swelling and soreness have disappeared. It is probable that 

 more permanent injuries result from careless treatment of 

 sprains than from all other accidents to the skeleton. 



10. A COMPARATIVE STUDY OF SKELETONS 1 



Skeletons of Invertebrates and of Vertebrates. We have 

 defined a vertebrate as an animal with a backbone, and an 



FIG. 80. Living Coral surrounded by its Outer Skeleton. 



invertebrate as an animal without a backbone. This dis- 

 tinction between the two subdivisions of the animal king- 

 dom can be carried still farther, and we may say that in 

 general the invertebrates either have no skeleton at all or 

 that, when present, the skeleton is on the outside of the 



1 See "Laboratory Exercises," No. 37. 



