160 Appendix. 



hour. Then setting them aside at ordinary temperatures, which 

 are favorable to the generation of infusoria, even after the lapse 

 of months not a trace of animal life could be found on breaking 

 the flasks. This was in the year 1775. But Needham was not 

 satisfied with these results, and with a show of reason claimed 

 that such a prolonged boiling would destroy not only germs, but 

 the germinative, or as he called it " vegetative force" of the in- 

 fusion itself. Spallanzini easily disposed of this objection by 

 showing that when the infusions were again exposed to the air, 

 no matter how severe or prolonged the boiling to which they 

 had been subjected, the infusoria reappeared. His experiments 

 were made in great numbers, with different infusions, and were 

 conducted with the utmost care and precision. The result seem- 

 ed convincing and was in substance that whenever animalcules 

 were found in infusions which had been exposed to great heat, 

 they "are not produced there because their germs have resisted 

 this temperature or because they have been generated spontane- 

 ously ; but because new germs have been introduced into the in- 

 fusion from the atmosphere after the boiling has ceased." 



The naturalists of this period almost without exception ac- 

 ceded to these conclusions, doubt being entertained on a single 

 point only. Oxygen had been discovered by Priestley in 1774, 

 and its relation to the maintenance of life was for many years 

 carefully studied by the physiologists. Now, might not the oxy- 

 gen in the air of the flasks have been in some way altered by the 

 high temperatures, and might not a renewal of oxygen be neces- 

 sary to the development of life under any circumstances ? This 

 certainly seemed reasonable, and so it became necessary to repeat 

 the experiments under conditions which would obviate these ob- 

 jections. This was done in 1836 and 1837 by Schultze and 



any method even on the assumption that all those preexisting within have 

 been destroyed may be appreciated when we recall the extremely minute 

 size even of the fully developed parent animal. The monas crepusculum for 

 instance is so small that eight millions of them would occupy a space no 

 larger than a grain of mustard seed, and Prof. Owen has. calculated that a sin- 

 gle drop of water may contain five hundred millions of them. Such organ- 

 isms would pass readily through imperceptible cracks or pores with changes 

 in the temperature of the surrounding atmosphere. 



