HISTORY OF ZOOLOGY 



657 



Figure 463. Gregor Johann Mendel (1822- 

 1884), who discovered the fundamental laws of 

 heredity. As a background for the portrait, Mr. 

 Flatter, the artist, has used a scene near Brno, 

 Czechoslovakia. 



were ignored until 1900, when three inde- 

 pendent investigators whose researches had 

 led them to the same conclusions that 

 Mendel had reached read his paper "Experi- 

 ments in Plant Hybridization" and an- 

 nounced its importance to the world. Thus, 

 although Mendel discovered the laws of 

 heredity to which his name is now attached, 

 modern genetics really dates from the year 

 1900. 



Louis Pasteur (1822-1895) (Fig. 464) 

 was a French chemist, a contemporary of 

 Mendel, who is best known for his dis- 

 coveries in the field of microbiology. By 

 proving that only living microorganisms 

 (yeast and bacteria) can cause fermentation, 

 he was able to suggest a method of pre- 

 venting this process by heating substances to 

 a temperature high enough to kill these 

 germs. This method of killing germs is now 

 known as pasteurization. Pasteur, in 1865, 

 saved the silk industry of France by discover- 

 ing how eggs containing parasites could be 

 distinguished from good eggs by means of a 



Figure 464. Louis Pasteur (1822-1895), the 

 French chemist who proved that fermentation and 

 putrefaction resulted from microbes, and thus put 

 an end to the controversy regarding the possibility 

 of spontaneous generation. (Courtesy of Fisher 

 Scientific Company.) 



microscope. Diseased eggs could thus be de- 

 stroyed and silkworms raised from good eggs 

 only. This discovery has saved the world bil- 

 lions of dollars. 



Hugo De Vries (1848-1935) (Fig. 465) 

 was a Dutch botanist who, after 20 years 

 of work, published a book on The Mutation 

 Theory. This theory was based largely on the 

 results of experiments with the evening 

 primrose Oenothera lamarckiana. Among his 

 plants he observed variations that bred true, 

 which he called mutations, and other varia- 

 tions which were not inherited. Most of the 

 changes observed by De Vries in the eve- 

 ning primrose were not gene mutations, 

 some represented chromosomal aberrations, 

 others polyploidy, and a considerable num- 

 ber were the result of unusual types of re- 



