314 THE BEGINNINGS OF LIFE. 



lower temperature than this. In dry air or in vacua, 

 therefore, we may look upon the temperature of J3OC 

 for thirty minutes, as marking the extreme limit, so 

 far as it has been hitherto possible to fix it, of vital 

 endurance under such conditions even for animals 

 which are covered by a tough chitinous integument. 

 There is, at present, no evidence forthcoming to shake 

 the validity of this conclusion. 



When immersed in fluids^ however, the power 

 possessed by the inferior organisms of resisting the 

 destructive influence of heat is not nearly so great. 

 Comparatively few, whether animal or vegetable, are 

 believed to be capable of resisting a temperature of 75 

 C (167 F) j and with regard to that of 100 C (212 F), 

 it has been admitted, by MM. Claude Bernard and 

 Milne-Edwards, by M. Pasteur, and by all the other 

 most influential opponents of the doctrines of arche- 

 biosis and heterogeny, that such a temperature, even 

 for one minute, has invariably proved destructive to all 

 the lower organisms met with in infusions 1 so far as 



1 It is quite fair to make this limitation, since we are only concerned 

 with the origin of such organisms. Seeds of higher plants, provided 

 with a hard coat, may especially after prolonged periods of desiccation 

 germinate even after they have been boiled for a long time in water. 

 This was ascertained by M. Pouchet to be the case with an American 

 species of Medicago. Some of the seeds were completely disorganised 

 by the boiling temperature, whilst a few remained intact, and it was these 

 latter which were afterwards found to germinate. They had been pro- 

 tected from the influence of the hot water by their very dry and 

 hardened coats. On this subject Prof. Jeffries Wyman says : ' Water 

 penetrates the seeds of many plants, and especially of some of the Legu- 



