2 PHYSIOLOGY. 



A living plant or animal is like a fountain into which and out 

 of which material is constantly passing, but the fountain maintains 

 its form and general appearance. Huxley's simile of a whirlpool in 

 a stream is very striking. The pool remains the same in the stream, 

 but water enters it, becomes a part of it as it is whirled around, 

 then passes out and gives place for other to enter. The pool retains 

 its identity all the while that its elements are being changed. 



The contrast between living and lifeless matter forms the basis 

 of the separation of the natural sciences into two divisions: the 

 biological and physical divisions, biology dealing with living and 

 physics with lifeless matter. 



Biology is the science that treats of living things, whether ani- 

 mal or vegetable, normal or abnormal. It deals with the forms, 

 structures, and origin, together with the functions and activities 

 of the whole animal or plant or its various parts. In fact, its scope 

 is so wide and comprehensive that it becomes necessary to divide 

 it into two branches : morphology and physiology. 



Morphology is that part of the science that deals with the form 

 and structure of living things, together with their arrangements. 



Physiology is the science that treats of the functions, or work, 

 of the various parts of the living organism, and what each one does 

 toward the economy of the whole. For instance, the study of the 

 form, growth, and development of the different parts of the brain, 

 beginning with the lamper-eel, then the higher fishes, birds, and 

 mammals, belongs to the science of morphology. By comparisons we 

 see that in the lamper there is merely the semblance of a brain in its 

 crudest form, showing no development as compared with the brain of 

 the higher fishes and birds. In the latter we notice a stronger 

 development in one department the optic lobes. The cerebral por- 

 tion is very weak. In mammals the reverse is true, and it reaches its 

 most striking size in man, in whom the cerebral portions are extremely 

 large and well developed, while the optic lobes are relatively small. 



The study of the functions, for instance, of the heart and kid- 

 neys belongs to the science of physiology; which tells how the heart 

 by its alternate contractions and relaxations forces the blood through 

 the circulatory system to the peripheral parts of the body for its sus- 

 tenance and nutrition and to the lungs for its purification by the 

 elimination of the carbonic acid and the absorption of the oxygen; 

 and how the kidneys by means of their mass of tubes and cells take 

 from the blood those parts that are no longer of any use, fit only 

 to be expelled from the body. When physiology is applied to man, 



