SEVENTEENTH AND EIGHTEENTH CENTURIES %^-J 

 wards entering the Genevan representative council and making a great rep- 

 utation both as a scientist and as a public citizen. He died in 1845. He was 

 both a chemist and a physicist, but he is chiefly known for his work on 

 vegetable physiology, spending years in the investigation of the subject and 

 finally publishing his results in 1804. The greatest service performed by this 

 work lies in the fact that here for the first time the quantitative method of 

 chemical research, as founded by Lavoisier, together with its results, were 

 systematically applied to living subjects of investigation. This opened up 

 for Saussure entirely new possibilities for methodically organizing his experi- 

 ments that his predecessors never possessed. He enclosed plants and parts of 

 plants in a quantity of air which had been previously weighed and carefully 

 analysed, and after having let them live there under different conditions, 

 in light and in darkness, he investigated the changes in the composition of 

 the air which their manifestations of life had brought about. He thus estab- 

 lished the quantitative relation between the amount of carbonic acid ab- 

 sorbed by the plant in light and the quantity of oxygen simultaneously 

 given off by it. In the same way he found out the quantity of oxygen absorbed 

 by a plant at night, and also the quantity of water consumed in association 

 with the absorption of carbonic acid that is required for the growth of the 

 plant. While the plant was thus found to derive the quantitatively most 

 considerable portion of its nourishment from the air, Saussure on the other 

 hand established the indispensability of the mineral constituents which it 

 drew from the earth, and which he determined by careful analyses of the 

 ashes of the plants investigated. Finally, he also found out that the per- 

 centage of nitrogen that the plants possess is primarily absorbed in the form 

 of ammoniac associations. On the other hand, Saussure was wrong in think- 

 ing, in contrast to Ingenhousz, that the green colour of the leaves is not 

 essential to their vitality — a misconception (based on the existence of red 

 leaves in certain varieties) that, owing to his authority, was long associated 

 with that line of research. 



But while Lavoisier's new method was thus immediately applied to 

 biology with a large measure of success, the more speculatively inclined 

 scientists were led by it to make bold guesses — as is usually so with new 

 discoveries. In the romantic natural philosophy we shall find ideas which 

 were awakened to life by the great revolution in chemistry. 



