SPONTANEOUS GENERATION 3 



degrees in different atmospheres, few in the pure air of the Mer de 

 Glace, more in the air of the plains, most in the air of towns. He 

 further proved that it was not necessary to insist upon hermetic 

 sealing or cotton filters to keep these living organisms in the 

 air from gaining access to a flask of infusion. If the neck of the 

 flask were drawn out into a long tuhe and turned downwards, and 

 then a little upwards, even though the end be left open, no con- 

 tamination gained access. Hence, if the infusion were boiled, no 

 putrefaction would occur. The organisms which fell into the open 

 end of the tube were arrested in the condensation water in the 

 angle of the tube ; but even if that were not so, the force of gravity- 

 acting upon them prevented them from passing up the long arm of 

 the tube into the neck of the flask. A few years after Pasteur's 

 first work on this subject, Tyndall conceived a precise method of 

 determining the absence or presence of dust particles in the air by 

 passing a beam of sunlight through a glass box before and after its 

 walls had been coated with glycerine. Into the floor of the box 

 were fixed the mouths of flasks containing an infusion. These 

 were boiled, after which they were allowed to cool, and might 

 then be kept for weeks or months without putrefying or reveal- 

 ing the presence of germ life. Here all the conditions of the in- 

 fusions were natural, except that in the air above them there was no 

 dust. 



The sum-total of result arising from these investigations was to 

 the effect that no spontaneous generation was possible, that the 

 atmosphere contained unseen germs of life, that the smallest of 

 organisms responded to the law of gravitation and adhered to moist 

 surfaces, and that micro-organisms were in some way or other the 

 cause of putrefaction. 



The final refutation of the hypothesis of spontaneous generation 

 was followed by an awakened interest in the unseen world of micro- 

 organic life. Investigations into fermentation and putrefaction 

 followed each other rapidly, and in 1863 Davaine claimed that 

 PoUender's bacillus of anthrax, which was found in the blood and 

 tissues of animals which had died of anthrax, was the cause of that 

 disease. From that time to this, in every department of biology, 

 bacteria have been increasingly found to play an important part. 

 They cause changes in milk, and flavour butter; they decompose 

 animal matter, yet build up the broken-down elements into com- 

 pounds suitable for use in nature's economy ; they assist in the 

 fixation of free nitrogen ; they purify sewage ; in certain well- 

 established cases they are the cause of specific disease, and in many 

 other cases they are the probable cause. No doubt the disposal of 

 spontaneous generation did much to arouse interest in this branch 

 of science. Yet it must not be forgotten that the advance of the 



