PRACTICAL RESULTS OF BACTERIOLOGY. 735 



THE PRACTICAL RESULTS OF BACTERIOLOGICAL 

 RESEARCHES.* 



BY GEOEGE M. STEENBEBG, M. D., LL. D., 



SURGEON GENERAL, U. 8. A. 



ENTLEMEN : In selecting a subject for my presidential 

 address I have thought it best to restrict myself to that 

 branch of biological science with which I am most familiar ; 

 and, as a technical paper might prove uninteresting to many of 

 those who constitute my present audience, I have chosen a title 

 for my address which will enable me to speak in a general way 

 of the development of our knowledge relating to the low vege- 

 table organisms known as bacteria, and the practical results 

 which have been the outcome of researches commenced in the 

 first instance solely on account of their scientific interest. 



Attention was first prominently called to the bacteria by the 

 investigations relating to spontaneous generation. It was gen- 

 erally believed prior to the researches of Spallanzini, in 1776, that 

 the development of micro-organisms in boiled organic fluids ex- 

 posed to the air was by heterogenesis. Spallanzini showed by 

 experiment that in some instances putrescible liquids when boiled 

 and kept in hermetically sealed flasks could be preserved indefi- 

 nitely without undergoing change. But he was not always suc- 

 cessful in this experiment. Bastian, and other supporters of the 

 theory of heterogenesis, at a later date, repeated these experi- 

 ments with similar results, and maintained that when a develop- 

 ment of micro-organisms occurred in a boiled fluid contained in a 

 hermetically sealed flask it could only be by spontaneous genera- 

 tion. But Pasteur, in 1860, gave the true explanation of the ap- 

 pearance of living bacteria under such conditions. He proved 

 that when development occurs it is because the organic liquid has 

 not been completely sterilized, and that certain micro-organisms 

 (spores of bacilli) withstand the boiling temperature, especially 

 when they are suspended in a liquid having an alkaline reaction. 

 At the present day this question is regarded as definitely settled, 

 at least so far as known conditions are concerned ; and we have 

 an exact experimental knowledge of the thermal death-point of 

 many micro-organisms of this class. 



The principal pathogenic bacteria are destroyed at tempera- 

 tures much below the boiling point of water. Thus, in experi- 

 ments made by the present speaker in 1885 it was ascertained that 



* Address of the President of the Biological Society of Washington, delivered Decem- 

 ber 14, 1895, under the auspices of the Joint Commission of the Scientific Societies of 

 Washington, 



