542 SPECIAL METHODS OF DISCOVERY. 



ments, made during the middle of the eighteenth century, 

 that Bonnet and Spalianzani discovered that if the horns, 

 tails, legs, eyes, or even the head of some creatures 

 including even garden snails were cut off, they would 

 grow again. The tail and legs of a salamander were 

 removed, and reproduced themselves as many as eight 

 times in succession. It has also been found, by means 

 of experiments, that the more simple the structure of an 

 animal is, the more do its several parts possess a power 

 of independent existence, and that in the more complex 

 animals the derangement of one part much more affects 

 the action of the entire organism. By putting two live 

 mice in a closed vessel filled with pure oxygen, Dr. 

 Priestley, about the year 1774, discovered that they lived 

 longer than in an equal volume of ordinary air ; he also 

 breathed pure oxygen, and felt benefited, and said, ' Who 

 can tell whether this pure air may not at last become a 

 fashionable luxury ? ' By confining some growing mint 

 in a vessel of air, the oxygen of which had been con- 

 verted into carbonic anhydride by combustion or breath- 

 ing, he discovered the important fact that the air was 

 again rendered fit to support combustion and life. Some 

 of the earliest experiments to discover the effects of gal- 

 vanism on animals were made by Fowler, in the year 

 1793. Sir Humphry Davy, by means of a series of ex- 

 periments upon himself, breathing particular vapours and 

 gases, and gradually increasing the duration of inspiration 

 of each, discovered the intoxicating effects of nitrous oxide 

 or ' laughing gas,' as it was afterwards called. 



The foregoing instances constitute only a small portion 

 of the discoveries selected out of the multitudes which 

 have been made by means of experiment. In nearly all 

 of them it must not be supposed that the discoveries were 

 completely made by experiment alone. Experiment was 



