INTRODUCTION 



hand, it must not be forgotten that, so far as is actually known, all 

 living organisms have arisen only from similar organisms. So far as 

 experience has shown, spontaneous generation is unknown. In olden 

 times it was a common supposition that all nature itself was endowed 

 with universal life. According to Aristotle, frogs and snakes sprang 

 from mud and slime. In the same degree that knowledge of the actual 

 development of living organisms was extended, the previously accepted 

 cases of spontaneous generation became more and more restricted, and 

 were finally limited to intestinal worms which could not otherwise, it 

 was thought, be accounted for, and to microscopic organisms the 

 origin of which was also not understood. Now, for such organisms 

 the possibility of a spontaneous generation has been disproved by more 

 modern investigations ; the history of the development of intestinal 

 worms is known, and the germs of organic life have been found to exist 

 everywhere. Schwann and Pasteur have been pioneers in this work, 

 and have shown that it is possible to hinder the development of the 

 lower organisms, in places where it is customary to find them, by 

 destroying all existing germs and at the same time preventing the 

 entrance of new ones. It is due to the results obtained by these 

 men in their investigations on spontaneous generation that we are now 

 able to preserve food in a scientific manner. The germs previously 

 existing in the substance to be conserved are destroyed by heat, 

 while, by a proper mode of sealing, the entrance of new germs is 

 rendered impossible, and the decomposition which their presence would 

 occasion is accordingly prevented. 



All known living organisms have been derived from other living 

 organisms. The attempt to relegate spontaneous generation to an un- 

 known field, and to admit the origin of living from dead substances, 

 has on the other hand derived support from the progress of chemical 

 research. In the early decades of the present century it was customary 

 to draw a distinct line of separation between organic and inorganic 

 chemistry, and to assume that the substances dealt with by organic 

 chemistry could only be produced by the vital action of organisms. 

 The laws governing inorganic chemistry appeared to have no refer- 

 ence to organic chemistry, the formation of organic substance being 

 due to a special force, the "life force." In 1828 Wohler obtained 

 urea from ammonium cyanate, and thus for the first time produced 

 an organic compound from an inorganic substance. In 1845 

 Kolbe completely synthesised trichloracetic acid, and in 1850 

 Berthelot synthesised alcohol and formic acid. By these results 

 the former distinction between organic and inorganic chemistry was 

 destroyed. Organic chemistry has become the chemistry of carbon 

 compounds. 



Botany, or the science of plants, may be divided into a general and 

 a special part. In the general part, the structure and functions of 

 plants as such will be considered ; in the special part, the particular 



