12 PRINCIPLES OF PHYSIOLOGY 



or an animal. Thus one of the higher plants 

 is rooted to the soil, from which it mainly 

 derives nourishment ; it spreads its branches 

 and leaves and flowers to the air, and it 

 breathes. An animal of the higher orders 

 shows active movements such as running or 

 leaping, it breathes, it requires food, and it 

 can produce heat. We find accordingly that 

 there are phenomena to be observed and 

 explained in both the plant and the animal. 

 It is the province of the physiologist to study 

 those phenomena and to offer explanations. 

 The field of work, however, is so immense that 

 the science naturally subdivides into plant and 

 animal physiology. The first is a division of 

 the science of Botany, while that of the latter 

 falls into the domain of the Zoologist. Thus, 

 in a sense, all the phenomena of living things 

 fall into those two sciences, but, by common 

 consent, the task of describing and explaining 

 the phenomena on which life depends, is 

 relegated to physiology, and this again may be 

 subdivided into the physiologies of the various 

 animals. We discuss the phenomena occur- 

 ring in the body of man as Human Physiology, 



