CHAPTER I 



INTRODUCTION 



Physiology is the branch of science which is concerned with 

 the functions performed by living things. It is a department of 

 Biology or the science of life. But just as Biology is divisible 

 into Botany which treats of plants, and Zoolog}^ which deals with 

 animals, so there nre also a Vegetable Phj'siology and an Animal 

 Physiology', and it is the latter of these which forms the basis of 

 medical and veterinary knowledge. For Physiology is the science 

 which teaches us the way in which the body is built up, and how 

 each part of it works, and the laws which govern its activities. 

 In so doing it helps us to regulate these activities, and by teach- 

 ing u^ about the normal working of the body, it shows us how 

 any of its parts may be adjusted when they are out of order. 

 This statement applies to the bodies of animals as well as to 

 those of ourselves. 



The present volume deals especially with the Physiology of 

 the domestic animals. This is a branch of the subject which has 

 been much neglected, for notwithstandmg the great industrial 

 importance of stock breeding and rearing, it is a business to 

 which physiological science has been applied but little. 



Like Chemistry and Physics, Physiology is founded on obser- 

 vations and experiments. These can sometimes be carried out 

 upon ourselves, but are more often made upon animals. By 

 means of a clinical thermometer we can perform a series of 

 observations upon our own bodily temperature, establishing the 

 fact that under normal conditions our temperature remains 

 constant and is independent of that of the outside air which 

 is usually considerably cooler. In this way w^e can learn a 

 little about the fundamental nature of the organism, since we 

 are led to perceive that our bodies like those of other animals 

 must be suppHed with the sources of that form of energy 

 which we recognise as bodily heat. By extending our obser- 

 vations, and noting the increased blood supplj^ of the skin and 

 the tendency to sweat when we feel warm, we learn something 



