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SCIENCE. 



[Vol. XII. No. 307 



demonstrated by experiment that micro-organisms may develop in 

 an organic liquid sterilized by heat ; but Pasteur showed that the 

 boiling temperature does not destroy all germs, and that to insure 

 sterilization of a neutral or alkaline medium a temperature of i io° 

 to 112° C. is required. The same savant first recognized the fact 

 that this failure to sterilize organic liquids by boiling at the ordi- 

 nary barometric pressure was due to the presence of reproductive 

 bodies, which he described under the name of ' brilliant corpuscles," 

 ' germs,' ' conidia,' etc. These spores had previously been seen by 

 Perty in 1852 and by Charles Robin in 1853, but it was not until 1876 

 that their mode of formation and true function were definitely estab- 

 lished by the German botanist Cohn. In the same year Koch pub- 

 lished in Cohn's Beitrdge ziir Biologie der Pflanze7t his admirable 

 memoir, ' Die Aetiologie des Milzbrandkrankheits,' in which he 

 showed that endogenous spores are produced, under certain cir- 

 cumstances, by the anthrax bacillus, and that these are true repro- 

 ductive bodies. In 1881 the same author published in the Mit- 

 theilungeii aiis dein Kazserlichen Gesundheitsamte his disinfection 

 experiments, in which these spores served as the test of the disin- 

 fecting power of heat and of various chemical agents. These ex- 

 periments showed that dry heat was very much inferior to moist 

 heat for the destruction of these bodies, and that when per- 

 fectly dry they resisted for several hours a temperature of 20° C. 

 above the boiling-point. To insure their destruction, a temperature 

 of 140° C, maintained for at least an hour, was found to be neces- 

 sary. When, however, the spores were immersed in boiling water, 

 or in steam given off from the same at the ordinary pressure of the 

 atmosphere, it was found that a few minutes sufficed to destroy the 

 vitality of these spores. 



The demonstration that the atmosphere constantly contains in 

 suspension the living ferments which cause putrefactive and fer- 

 mentative changes in organic liquids led to the belief, still enter- 

 tained by many who are not familiar with our bacteriological 

 methods, that the slightest exposure must insure the entrance into 

 such a liquid of these ubiquitous germs. 



Pasteur first showed that the liability to contamination by a brief 

 exposure to the air is by no means so great as had been generally 

 supposed, and that, as a matter of fact, a putrescible liquid rarely 

 becomes infected by such exposure as occurs in the ordinary lab- 

 oratory operation of removing the cotton air-filter for the purpose 

 of inoculating a culture. This is now a matter of every-day labo- 

 ratory experience ; and the fact, also demonstrated by Pasteur, that 

 upon the surface of objects, and especially in accumulations of 

 dust, these living ferments abound in great numbers, is now gen- 

 erally recognized. 



Up to the time of Cohn, botanists had paid but little attention to the 

 minute vegetable organisms under consideration ; and but for the 

 discovery that some of them invade the human body as parasites, 

 and thus give rise to fatal forms of infectious disease, it is probable 

 that we would still be ignorant of their real characters. The earlier 

 botanists had no conception of the great number of species exist- 

 ing, — species which we now know are in many instances as well 

 defined, and apparently as permanent in their characters, as is the 

 case with plants higher in the scale of living things. The older 

 botanists generally adopted the view that these low organisms are 

 polymorphous, and that there are but a small number of distinct 

 species. Indeed, until the illustrious German bacteriologist and 

 physician gave us a reliable method for isolating the various forms 

 which are commonly associated in putrefying infusions, it was im- 

 possible to determine what relation the little spheres, rods, and 

 spiral filaments revealed by the microscope might bear to each 

 other. Since Koch's methods have been employed by industrious 

 investigators in all parts of the world, we have commenced to learn 

 something of the bacterial flora; and it is apparent that the number 

 of distinct species is enormous. — comparable, for example, with 

 the number of well-defined species of diatoms, desmids, or other 

 classes of Algce higher in the scale. This flora is no doubt differ- 

 ent in different parts of the world, although some species are widely 

 distributed, and we may expect to discover many new forms when 

 bacteriologists extend their researches to distant portions of the 

 globe, and especially in the tropics. Already extended researches 

 have been made, especially in Germany, with reference to the bac- 

 terial flora of the soil, of streams and wells, and of the atmosphere ; 



but this line of research may be said to be still in its infancy, and 

 what has been done only serves to indicate the extent of the field 

 and the amount of work which remains to be done before our 

 knowledge will be complete. The same may be said of the bac- 

 terial flora of the intestine of man and of the lower animals. Here 

 we have not only to determine the constant species, as distinguished 

 from the accidental, and in some cases no doubt pathogenic forms, 

 but we have also to determine the physiological role of each con- 

 stant form ; for we can scarcely doubt that these commensals of 

 man, which help to disintegrate the organic pabulum introduced 

 into the alimentary canal, and give rise to the formation of a variety 

 of chemical products, some of which are known to be toxic, play 

 an important part in the economy of the individual. 



With the methods now at our command, these questions, and 

 those relating to the physiological characters of pathogenic species, 

 are open to investigation. But let me warn the young bacteriolo- 

 gists of to-day not to plume themselves too much upon the scientific 

 achievements which await them in the application of these methods, 

 and to remember that the serious errors which in the past have 

 been made by many of the pioneers in this field of investigation 

 were in many instances due, not to an inferior degree of intelligence 

 or a less earnest desire to get at the exact truth, but to the difficul- 

 ties which they encountered in a new field of investigation, in which 

 satisfactory methods of research were not yet developed. 



The great impetus which bacteriological studies have received 

 since the introduction of Koch's plate-method and the use of solid 

 culture-media, is shown by the recent literature of the subject. 

 Prior to this date (1881) the number of active workers in the field 

 was small, and much of the work done had little scientific value 

 from our present point of view. Morphological differences were 

 the chief reliance for differentiating species, but we now know that 

 such distinctions are entirely unreliable. Many species which have 

 important and permanent physiological characters, which serve to 

 distinguish them in a definite manner, are practically identical in 

 their morphology. Thus, for example, no bacteriologist would at- 

 tempt to decide, by a microscopical examination alone, whether a 

 coccus obtained from the pus of an acute abscess was the staphy- 

 lococcus aureus, citreus, or albus ; but the growth upon a solid 

 culture-medium would decide the matter by the characteristic color 

 of the mass developed about the point of inoculation. A great part 

 of the work to be done in bacteriological laboratories consists in 

 this differentiation of species, and in defining in an exact manner 

 the biological characters of each, including mode of growth in vari- 

 ous media, resistance to chemical agents and to heat and cold, 

 pathogenic power, etc. 



As indicating the progress in this department of science and the 

 character of the work already done, I propose to make a brief 

 analysis of the literature of the subject. In a bibliography at hand, 

 which is quite full without being complete, I find reference to 41 

 papers published prior to the year i860. Of these, 7 are in Ger- 

 man, 31 in French, and 3 in English. During the decade from 

 i860 to 1870 the same bibliography gives the titles of 55 papers, of 

 which 8 are in German, 43 in French, 3 in Italian, and I in English. 

 The following decade, 1870 to 1880, shows a very greatly increased 

 activity in this field of research ; and among the titles given we 

 have in Germany papers by Buchner, Billroth, Cohn, Eberth, 

 Frisch, Hiller, Klebs, Koch, Letzerich, Nageli, Orth, Pragmowski, 

 Weigert, Wernich, and others. In France the most prominent 

 names during this period are those of Arloing, Cornevin, and 

 Thomas, Bechamp, Paul Bert, Bouley, Chauveau, Colin, Davaine, 

 Donne, Felz, Miquel, Pasteur, Van Tieghem. and Toussaint. In 

 England the most important contributions during the same period 

 were by Bastian, Beck, Cunningham, Dallinger, Dougall, Klein, 

 Lewis, Lister, and Sanderson. The total number of titles included 

 in my bibliography is 329, of which 122 are German, 121 French, 

 57 English, and 9 Italian. From this time the interest in this field 

 of investigation, as shown by the literature in which experimental 

 investigations are recorded, has very rapidly increased. My bibli- 

 ography gives the titles of 92 papers published during the year 1881, 

 of which 27 are in German, 45 in French, 16 in English, and 4 in 

 Italian. 



Passing over the years 1882, 1883, and 1884, I take from the 

 valuable ' Jahresbericht ' of Baumgarten, first published in 1885. 



