SYNOPSIS OF PHYSIOLOGY 



CHAPTER I 



INTRODUCTION 



M When a single-celled organism such as Amoeba is studied 

 it is found to possess certain features which distinguish 

 it from non-hving things. (1) It is able to change its 

 shape, to envelop particles of food-material and to move 

 from place to place. These functions it performs by 

 virtue of the contractility of the protoplasm of which 

 it is composed. (2) It responds in an active manner to 

 certain stimuli. It has therefore the property of irrita- 

 bility. (3) It has the power of ingesting or dissolving 

 particles of certain organic substances and of incorporating 

 them into its own architecture. This is the process of 

 assimilation or anabolism. (4) It is also able to oxidise 

 the complex substances formed in anaboUsm. This pro- 

 cess is known as catabolism, the combined processes of 

 anabohsm and catabolism being termed metabolism. (5) It 

 is able to expel from its body certain substances. These 

 are of two kinds — particles which it has enveloped but 

 cannot digest, and end-products of the catabolic changes. 

 This function is known as excretion. (6) Lastly, it has 

 the capacity for reproducing itself. 



These fundamental properties are found also in multi- 

 cellular animals, but with this difference, that in the latter 

 the different cells of which the individual is composed 



