6 HISTORICAL. 



The development of our knowledge relating to the bacteria, 

 stimulated by the controversy relating to spontaneous generation 

 and by the demonstration that various processes of fermentation 

 and putrefaction are due to microorganisms of this class, has 

 depended largely upon improvements in methods of research. 

 Among the most important points in the development of bacterio- 

 logical technique we may mention, first, the use of a cotton air 

 filter (Schroder and Von Dusch, 1854) ; second, the sterilization of 

 culture fluids by heat (methods perfected by Pasteur, Koch, and 

 others) ; third, the use of the aniline dyes as staining agents (first 

 recommended by Weigert in 1877) ; fourth, the introduction of 

 solid culture media, and the ' ' plate method " for obtaining pure cul- 

 tures, by Koch in 1881. 



The various improvements in methods of research, and espe- 

 cially the introduction of solid culture media and Koch's "plate 

 method" for isolating bacteria from mixed cultures, have placed 

 bacteriology upon a scientific basis, and have shown that many of 

 the observations and inferences of the earlier investigators were 

 erroneous owing to the imperfection of the methods employed. 



Since it has been demonstrated that certain infectious diseases of 

 man and the lower animals are due to organisms of this class, phy- 

 sicians have been especially interested in bacteriological researches, 

 and the progress made during the past fifteen years has been largely 

 due to their investigations. It was a distinguished French physi- 

 cian, Davaine, who first demonstrated the etiological relation of a 

 microorganism of this class to a specific infectious disease. The an- 

 thrax bacillus had been seen in the blood of animals dying from this 

 disease by Pollender in 1849 and by Davaine in 1850, but it was sev- 

 eral years later (18G3) before the last-named observer claimed to 

 have demonstrated by inoculation experiments the causal relation of 

 the bacillus to the disease in question. 



The experiments of Davaine were not generally accepted as con- 

 clusive, because in inoculating an animal with blood containing the 

 bacillus, from an infected animal which had succumbed to the 

 disease, the living microorganism was associated with material 

 from the body of the diseased animal. This objection was subse- 

 quently removed by the experiments of Pasteur, Koch, and many 

 others with pure cultures of the bacillus, which were shown to have 

 the same pathogenic effects as had been obtained in inoculation ex- 

 periments with the blood of an infected animal. 



The next demonstration of the causal relation of a parasitic mi- 

 croorganism to an infectious malady was made by'Pasteur, who de- 

 voted several years to the study of an infectious disease of silkworms 

 which threatened to destroy the silk industry of France pebrine. 



