WHAT IS AN ORGANISM? 1 77 



structure and differentiation of parts, called organs, and of 

 the specialization of the functions of these organs 



Classification of the Functions of a Vertebrate. Analysis of a 

 highly specialized organism, such as a vertebrate, presents us 

 with three groups of functions, viz. ; Sustentation, Genera- 

 tion, and Correlation. 



L Sustentation, or Assimilation, is seen in the various 

 processes of what we are accustomed to call growth, the tak- 

 ing in and digesting of food, and the building up of tissue. 



In assimilation two kinds of results are attained. The 

 morphologic effects are technically called metabolic changes; 

 these may be divided into changes of two kinds : Constructive, 

 or Anabolism ; and Destructive, or Katabolism. The destruc- 

 tive process, or katabolism, results in two special functions: 

 Secretion, which is the preparation of products necessary to 

 the anabolism, or to the constructive work of the organism ; 

 and Excretion, or throwing off of useless products of the 

 activities of the organism. 



II. Generation, or Reproduction vegetative multiplica- 

 tion. 



III. Correlation, exhibited in higher organisms in two 

 ways ; as (a) Contractility seen in muscular action, and 

 (b) Irritability as seen in responses to any exciting cause 

 or sensation. 



In the following table is shown the relation of the systems 

 of organs and special tissues to these groups of functions : 



I. SUSTENTATION. 



(I tt ) Nutritive ...... Alimentary system : mouth, stomach, intestines, etc. 



(I b ) Circulative ...... Circulatory system : heart, veins, etc. 



(Excretory organs : kidneys. 

 nO Purificative J Respiratory organs : lungs, etc. 



j Secretory organs : liver, salivary gland, pancreas, 



[ etc. 



i Generative organs : ovaries, etc. 

 Auxiliary organs : egg-capsules, uterus, mammae, 

 etc. 

 111. CORRELATION. 



f Muscles. 



/TTTa* /- Skeletal parts : exo- and endo-skeleton, for fixation 



1 1 support, protection, and offence, as teeth, clawsi 

 (_ bones, shell, coral, etc. 



Irritability \ Nerve-ganglia : nerves and brain. 

 itaoiuty - organs . eye> eafj etc 



