METHODS 9 



which, taken together, are wanting in not-living matter. 

 All these characters taken together ought to make up a defini- 

 tion of life, since it is their presence or absence which leads 

 us to pronounce a body living or not ; and if the definition 

 is well made it ought to permit of a strict classification of all 

 natural bodies a classification in which no ambiguity should 

 remain, so that a given body would fall necessarily under 

 one or other of the defined categories, living or not-living. 

 The comparative sciences of which we have already spoken 

 (comparative anatomy, physiology, embryology), in the long 

 run as living beings further and further remote are com- 

 pared together, ought to permit of the building up of a 

 Biology. For this it is enough to find in each living being 

 something which remains common to all in the progres- 

 sive extension of the groups we study, until we come to one 

 group that comprises in itself the sum total of characters 

 common to both the animal and vegetable kingdoms. 



Now, with the old definition of the word " anatomy " it 

 was evident that comparative anatomy could never lead to 

 any notion common to all living beings taken together. 

 Anatomy indeed was given up to the study of the different 

 parts which could be distinguished by the naked eye or with 

 the magnifying glass in animals and plants ; and there was 

 no need of being a great scholar to remark the want of like- 

 ness between the bones, muscles, and nerves of the dog on the 

 one hand and the stamens, pistil, and leaves of the straw- 

 berry plant on the other. Comparative anatomy was neces- 

 sarily limited to restricted groups such as vertebrates or 

 mollusks. 



The perfecting of instruments of study, particularly of the 

 microscope, has made it possible for students to penetrate 

 more deeply and intimately animal and vegetable structures. 

 The first important conquest of biology, due to the perfecting 



