THE ZOOLOGICAL POSITION OF THE DOG. H 



powers of rapid locomotion, capacity to perceive what 

 makes for its interest, and ability to utilize means to attain 

 this when perceived. These considerations demand that 

 an animal high in the scale of being shall be provided 

 with limbs sufficiently rigid to support its weight, moved 

 by strong muscles, which must act in harmony. But this 

 implies abundance of nutriment duly prepared and regu- 

 larly conveyed to the bones and muscles. All this would 

 be useless unless there was a controlling and energizing 

 system capable both of being impressed and originating 

 impressions. Such is found in the nerves and nerve- 

 centers. Again, in order that this mechanism be kept in 

 good running order, the waste of its own work (metabol- 

 ism), which chokes and poisons, must be got rid of hence 

 the need of excretory apparatus. In order that the nerv- 

 ous system may get sufficient information of the world 

 around, the surface of the body must be provided with 

 special message-receiving offices in the form of modified 

 nerve-endings. In short, it is seen that an animal as high 

 in the scale as a mammal must have muscular, osseous 

 (and connective), digestive, circulatory, excretory, and 

 nervous tissues ; and to these may be added certain forms 

 of protective tissues, as hair, nails, etc. 



The whole physiological story for one of the higher 

 animals, including the dog, may be thus told in brief : 



The blood is the source of all the nourishment of the 

 organism, including its oxygen supply, and is carried to 

 every part of the body through elastic tubes, which, con- 

 tinually branching and becoming gradually smaller, ter- 

 minate in vessels of hair-like fineness in which the current 

 is very slow a condition permitting that interchange be- 



