4 AN INTRODUCTION TO ZOOLOGY 



Before leaving this question of classification we may 

 glance at the somewhat misleading way in which the terms are 

 ordinarily applied in Universities and Colleges. Owing to the import- 

 ance of one animal, Man, and the fact that a medical training is 

 intended to give the student some detailed knowledge of this species 

 in particular, it is customary to take the general terms Anatomy, 

 Histology, Physiology, etc., and apply them to Man. They would 

 be more accurate if they had prefixed to them the word Human, 

 and so read Human Anatomy, etc., as is sometimes done. Then, 

 too, in the case of the terms Biology, Zoology and Botany, it is 

 obvious that a junior student cannot be expected to know the 

 whole of the ground covered by any one of these. So the terms 

 come to be used as convenient ones for indicating courses of study 

 that endeavour to give, often by the utilisation of certain types, 

 an introduction to the elementary fundamental ideas underlying 

 the Morphology, Physiology and Aetiology of animals or plants, 

 or both. 



Life. 



We have spoken of the division of material objects into 

 living or animate and non-living or inanimate, and it is necessary 

 to consider further what we mean by the word " living." Living 

 things are characterised by the possession of " life/' and, furthermore, 

 we only know of " life " as a manifestation of such beings. It is 

 a matter of great difficulty to give a concise and satisfactory defini- 

 tion of life, although we all of us know more or less clearly what it 

 implies, and it is brought most strikingly to our notice when it 

 ceases, and a living being becomes dead. 



It is unnecessary to attempt to define life, since for our purposes 

 it will be sufficient to become familiar with its more important 

 manifestations which we distinguish as vital phenomena, some of 

 the most obvious of which we make use of in determining whether 

 a thing is alive or lifeless. The most striking are those that concern 

 the activities of living things, and so fall under the heading of 

 physiology. 



Irritability. 



If we poke a stone that is firmly seated nothing happens, 

 yet, on the other hand, if we perform the same experiment on a 

 living animal it would most probably -make some movement In 

 reply, the nature of the reply depending on the animal. Here, in 

 a crude way, we have utilised one of the characteristic vital activities 

 to determine whether a thing is living or not, and we shall consider 

 briefly what it involves. In the case of the stone nothing happens, 



