THE VITAL PROPERTIES OF THE CELL 95 



The protoplasm of organisms which live in hot springs is able 

 to sustain much higher temperatures. Cohn found specimens of 

 Leptuthrix and Oscillaria in the Karlsbad springs at 53 C., whilst 

 Ehrenberg observed Alg in the warm springs of Ischia. 



But even in these cases we have not arrived at the extreme limit 

 of heat which can be sustained for a time by living substance. For 

 endogenous spores of Bacilli, which are furnished with unusually 

 resistent envelopes, remain capable of germination after they have 

 been heated for a short time in a liquid at a temperature of 100. 

 Many even can endure 105-130 (de Bary IV. 56, p. 4). It is only 

 after a substance has been exposed to the action of dry heat of 140 

 for a period of three hours that we can assume with certainty that 

 all life has been completely destroyed in it. 



It is even more difficult to determine the lower limit at which 

 " death from cold " occurs. As a rule, temperatures below are 

 less injurious to protoplasm than high ones. It is true that if the 

 eggs of Echinodermata, which are about to divide, are placed in a 

 freezing mixture at a temperature of from 2 to 3 C., the pro- 

 cess of division is temporarily arrested (IV. 12) ; but division 

 recommences and proceeds in a normal fashion when the eggs are 

 slowly warmed, even if they have been kept in the freezing mix- 

 ture for a quarter of an hour. Indeed, the greater number of 

 the eggs are found to be uninjured even if they have been kept 

 at this temperature for two hours. Plant-cells may be frozen 

 until ice crystals develop in the sap, and yet, after they have been 

 thawed, they exhibit the streaming movements of protoplasm 

 (IV. 15). 



Sudden exposure to temperatures below zero produces striking 

 changes of form in the protoplasm of plants ; however, it reverts 

 to its normal condition on being thawed. When Kiihne (IV. 15) ex- 

 amined in water cells of Tradescantia, which had been kept for 

 a little more than five minutes in a freezing mixture at 14 C., he 

 found, in the place of the ordinary protoplasmic net, a large number 

 of isolated, round drops and globules. These, after a few seconds, 

 began to show active movements, and in a few minutes commenced 

 to join themselves one to another, and thus to gradually become 

 reconstructed into a network, in which active streaming movements 

 soon commenced to take place. 



Kiihne describes in the following words another experiment: 

 " If a preparation of Tradescantia cells is kept for at least one 

 hour in a space which is maintained by means of ice at a tempera- 



