CH. xxiv. COMPARATIVE ANATOMY. 197 



much time upon each minute structure, that in seventeen 

 years, with all the help he had, he was not able to complete 

 the description of the whole human body. 



Haller discovers the Power of the Muscles to Contract. 

 It was while he was at work at these dissections that he 

 made one great discovery, which you must try to understand. 

 If you clasp your right hand round your left arm, just above 

 the elbow, and then bend your left arm, you will feel the 

 part under your hand swell up and grow hard. The reason 

 of this is that the muscle of your arm, called the biceps, has 

 contracted, or grown shorter and thicker, in the process 

 of bending your arm. If you open your arm again, the 

 swelling will go down, because the muscle is stretched out. 

 Now before Haller's time it was thought that the muscles 

 could not contract of themselves, but were drawn up by the 

 nerves. Haller discovered that this is not so, but that a 

 muscle, if irritated, will draw itself together even when it is 

 quite separated from the nerves, and this has since been 

 proved to be true by a great number of experiments. So 

 that though it is true that our nerves are the cause of our 

 moving, because they excite the muscles and so make them 

 contract, yet the real power of contraction is in the muscle 

 itself. 



Comparative Anatomy, or the Comparison of Different 

 Structures in Men and Animals. John Hunter. Another 

 point in which Haller did good service to science was in 

 comparing the same parts of the body of men and animals, 

 and showing how far they are alike. This study, which is 

 called the study of comparative anatomy, has now become 

 very important, for by examining any organ, such as the 

 heart for example, from the lower animals in which it is 

 very simple, up to man in whom it is complicated, we can 



