1896.] MICROSCOPICAL JOURNAL. 119 



by the investigations relating to spontaneous generation. 

 It was generally believed prior to the researches of 

 Spallanzini, in 1776, that the development of micro- 

 organisms in boiled organic ilaids exposed 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 

 indefinitely without undergoing change. But he was 

 not always successful in this experiment. Bastian, and 

 otlier supporters of the theory of heterogenesis, at a 

 later date, repeated these experiments with similar re- 

 sults, and maintained that when a development of micro- 

 organisms occurred in a boiled fluid contained in a her- 

 metically sealed flask it would only be by spontaneous 

 generation. But Pasteur, in 1860, gave the true 

 explanation of the appearance of living bacteria under 

 such conditions. He proved that when development 

 occurs it is because the organic liquid has not been com- 

 pletely 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 experi- 

 imental knowledge of the thermal death-point of many 

 micro-organisms of this class. 



The principal pathogenic bacteria are destroyed at 

 temperatures much below the boiling point of water. 

 Thus, in experiments made by the present speaker in 

 1885 it was ascertained that the cholera spirillum is 

 is destroyed by ten minutes' exposure to a temperature 

 of 52° C; the typhoid bacillus by 56°; the micrococcus of 

 pneumonia by 52°; the streptococcus of erysipelas (S pyog- 

 enes) by 64°; etc. According to Loefller, the bacillus of 

 glanders is destroyed in ten minutes by a temperature of 



