2 INTRODUCTION TO GENERAL PHYSIOLOGY 



" general " physiology should be confined to those properties which 

 belong to all living creatures. But this is not the meaning taken 

 here, because it would give us too limited an outlook. It is really 

 impossible to make a distinction between general and human 

 physiology. Perhaps the best way to explain the difference is 

 that it is the manner in which the subject is treated, rather than 

 the subject-matter itself. Thus, instead of taking an organ, such 

 as the liver, and talking about all the different things that it does, 

 we intend to discuss the processes in which it plays its part along 

 with other organs. This will become clearer as we go on, together 

 with the fact that whatever name we give to the particular form in 

 which the phenomena are presented, they are themselves always 

 the same. 



Just as physics and chemistry deal with the laws of inanimate 

 nature, apart from and necessarily before their application to 

 practical industry, so there is a body of science dealing with living 

 nature, which is a necessary preparation for application to the 

 human body. But it would exist as a science quite independent 

 of an}' such application. The reader may be reminded, especially 

 if he is inclined to overrate the importance of what is obviously of 

 immediate practical use, that it is not possible to know beforehand 

 what and when pure scientific knowledge may become suddenly of 

 the greatest practical value. Electric waves in physics, and the 

 electrical phenomena of the heart in medical science, may be taken 

 as two of the numerous instances of the kind. 



Protoplasm 



Like every other machine, a living organism does its work 

 because it is made in a certain way. We must know its structure, 

 therefore. And, first of all, let us see what is the simplest structure 

 that we can call " living." 



There are some minute creatures that consist only of a sub- 

 stance which has the appearance of a clear jelly, at first sight. 

 But when we look at it more closely under the microscope, we 

 see that it changes its shape, whereas a little lump of jelly would 

 _not do so. This material, which is known as " protoplasm," 

 lx^\aves more like a drop of oil in water, except that it seems to 

 have t!i; ;><>wer of movement on its own account. 



The organism called Amceba is composed of such protoplasm, 

 but it also contains some other things floating in its body-sub- 

 stance (E., p. 164). The "nucleus" may be noticed particularlv, 

 a spherical structure in one part or other of the protoplasmic mass. 

 There are also particles and drops of liquid of various sizes and 





