130 SPONTANEOUS GENERATION. 



germs, had already been demonstrated by M. Pasteur through exposing 

 infusions with perfect immunity from infection, to the open air of the 

 Mer de Glace, which experiment, with precisely identical results, was 

 repeated by Professor Tyndall in the vicinity of the Bel Alp at an elevation 

 of 7000 feet above the sea, in July of the year 1877. Respecting the 

 capacity of Bacteria and atmospheric germs to resist exposure to abnormal 

 elevations of temperature, he found the widest divergence to obtain in 

 materials derived from different sources or in different conditions of vitality. 

 Where the fully developed and vitally active organisms were experimented 

 on, contact with boiling water, or sometimes a temperature considerably 

 below ebullition, was found sufficient to deprive them of life, but where the 

 desiccated germinal matter was operated on, the results were as a rule 

 entirely reversed. In some few instances these germs were so tender 

 as to succumb to boiling for a term of five minutes, or even less, while in 

 extreme cases they were found sufficiently obstinate to survive a similar 

 ordeal of no less than eight hours' duration. As regards their respective 

 "death-points," or limit of heat-resistance. Professor Tyndall suggests that 

 the infusorial germs of the atmosphere might be conveniently classified under 

 the following heads : " Killed in five minutes ; not killed in five minutes, 

 but killed in fifteen ; not killed in fifteen minutes, but killed in thirty ; not 

 killed in thirty minutes, but killed in an hour ; not killed in an hour, but 

 killed in two hours ; not killed in two, but killed in three hours ; not killed 

 in three, but killed in four hours." Several cases of survival after four, five, 

 six, and even eight hours' boiling were met with, and as he further remarks, 

 there is no valid warrant for fixing upon eight hours as the final limit. 



The germinal dust obtained from long preserved, and thoroughly desic- 

 cated, hay was in all instances found to yield the most obstinately resisting 

 material, and the presence of a truss of hay anywhere in the vicinity of the 

 germinal matter experimented on, always constituted an important factor 

 in its reduction by boiling to a condition of sterility. Notwithstanding, 

 however, the great resistant property possessed by a large number of these 

 germs, Professor Tyndall has shown that even the most obstinate can 

 be sterilized or killed if certain precautions are taken in their treatment. 

 These consist of setting aside the infusion containing them, after ebullition, 

 in a warm room for a period of ten or twelve hours, then raising it again to, 

 and maintaining it for a short interval at, the boiling point, repeating the 

 process with similar intervals of rest several successive times. By these 

 means the germs as they approach their point of final development are 

 successively killed off in the order of their resistance, and the liquid is in the 

 end completely sterilized. 



The special chambers improvised by Professor Tyndall for the conduct 

 of the experiments above recorded recommend themselves so strongly, 

 on account of their simplicity of form and efficiency in action, both for 

 further experiments in a similar direction, and for the cultivation of Infu- 

 soria generally, that an illustration of one constructed to hold six test- 



