[Chap. XLII THE BIOLOGY OF BACTERIA 529 



do not arise spontaneously from meat. From the time of Redi to that 

 of Pasteur many critical experiments were performed. One result of 

 these experiments was the gradual abandonment of the idea that plants 

 and animals like those on the earth today arise by spontaneous gen- 

 eration. Progress in understanding the origin of living organisms, and 

 in following certain practices, such as those of sanitation, personal hy- 

 giene, aseptic surgery, and the preservation of food, was seen to depend 

 upon other ideas and upon further discoveries. 



Even more impressive than all these earlv experiments are the facts 

 known todav about the composition, organization, and correlations of 

 the parts of living cells, and of multicellular organisms. That such 

 highly organized structures could arise suddenly from either inorganic 

 or organic masses of matter appears quite untenable. Even if non-living 

 colloidal masses of organic matter ever attain tlie state of being alive, 

 escape destruction, and multiply, a very long geological period of time 

 would elapse before highly organized cells capable of exact duplication 

 by reproduction could evolve. After considering pertinent data from all 

 fields of science for 25 vears, Oparin came to certain conclusions about 

 the probable origin of living organisms on the earth, and clearly sum- 

 marized the data and conclusions in a small book which is cited at the 

 end of this chapter. 



Pasteur's experiments were not limited to the question of spontaneous 

 generation. He studied vinegar-making, silkworm diseases, rabies, and 

 diseases of sheep and cattle. He not only showed that bacteria and 

 other microorganisms cause diseases, but he developed methods of 

 vaccination that made man and other animals immune or at least less 

 susceptible to certain diseases. Perhaps one of the most touching stories 

 in all biologv is that of Pasteur's treatment of the little boy who was 

 bitten by a mad dog. 



Modern bacteriology. Out of the experiments of Pasteur and equally 

 significant ones by Koch (1843-1910), Lister (1827-1912), and many 

 others, the modern techniques used in the control of pathogenic or- 

 ganisms have developed. Bacteriology is now an important biological 

 science with many specialized phases of research in medicine, den- 

 tistry, veterinary medicine, agriculture, dairy technique, plant pathology, 

 and manv industrial processes. 



Methods of killing and controlling bacteria. It was known long before 

 bacteria were discovered that certain practices are valuable in the 

 preservation of foods, caring for wounds, and the prevention of disease. 



