FUNCTIONS OP ANIMALS. 15 



capillaries, which have an average diameter of only -^Vo of 

 an inch, have walls of extreme tenuity, which allow, with 

 the utmost freedom, the transition of materials outwards and 

 inwards between them and the surrounding textures. 



Reproduction is the function by means of which new in- 

 dividuals are developed from portions of pre-existing living 

 beings; and, although it is not generally so diffused through- 

 out the body as the function of nutrition, but is delegated to 

 special parts, yet it may be remarked that in many low 

 forms of animal life, and some even of the higher vegetable 

 forms, a large amount of reproductive power pervades the 

 entire organism. Also, in the higher animals there exists 

 an ill-understood connection between the reproductive organs 

 and the nutrition of the body generally, which is of a two- 

 fold description; the nutrition of the body being importantly 

 modified by the condition of these parts, and the minute 

 peculiarities of all parts of the body being capable of trans- 

 mission to the offspring. 



Sensation is a psychical, and not a physical condition ; 

 but it is associated and bound up with changes in the body, 

 the seat of which is the nervous system. The mind is not 

 influenced by external objects, save when these irritate 

 nerves or organs of sense into a state of activity, and the 

 active condition, travelling along nerve-trunks, reaches the 

 part of the brain with which the mind is specially and in- 

 scrutably linked. And not only is an active condition of 

 the brain necessary to influence the intelligence by external 

 objects, but a like active^ condition accompanies all emotion 

 and every operation of the mind. 



Movement of a voluntary description is accomplished by 

 muscles receiving, through nerves, their stimulus to action 

 from the brain, which in turn is stimulated in an unknown 

 way by the will. Thus, the central nervous system is both 

 the terminus to which messages from the organs of sense are 

 sent, and that from which commands to the voluntary muscles 

 proceed. 



All sensory function, however, is not sensation, and all 

 movement is not voluntary. The nervous system may 

 receive an influence from without, and transmit it to groups 

 of muscles, without intervention of any act of consciousness. 



