

THE VITAL PHENOMENA OF CELLS 29 



with different cells and may be gradually changed more or less for each 

 particular cell by training. 



For most animal and plant cells the upper limit of temperature compatible 

 with life is from 40 to 47 C. They die if they be subjected even for a short 

 time to a temperature a little higher than this, owing partly at least to the 

 coagulation which takes place at this temperature. And yet there are cells 

 which are able to endure a considerably higher temperature. In the hot 

 springs of Ischia, Alga? live at a temperature of 53 C., and it is said that 

 between the filaments of Oscillaria, ciliate Infusoria and Rotatoria survive a 

 temperature of 81 to 85 C. (Ehrenberg). Many Bacteria thrive at a tem- 

 perature of 50-55 C. or even as high as 72 C. ; and still more resistant 

 against heat are their spores, a dry heat of 140 C. maintained for at least 

 three hours being necessary to destroy life in them with absolute certainty. 



With regard to the lower limit of temperature compatible with life, it has 

 been found that Amoebae placed upon ice will cease all movements and remain 

 quiescent until the temperature is raised. If however they be frozen up in 

 drops of water, warming fails to revive them. 



A temperature below C. is not necessarily fatal for the cell. Pictet 

 observed with certainty that fish which had been cooled in a block of ice to 

 15 C. survived after carefully raising the temperature, although their 

 companions while frozen could be reduced to powder like ice. Fish which 

 were cooled to 20 C. could not be revived. Frogs survived a temperature 

 of 28 C., and myriopods 50 C. Seeds of cereals do not lose their power 

 of germination if they be subjected for a long time to a temperature of 

 -42 C. (C. de Candolle). Cholera spirilla and anthrax spores can be kept 

 alive for from twenty hours to seven days at the temperature of liquid air" 

 ( 183 to 192 C.). Indeed one species of Bacterium (B. phosphorescens) 

 survived a period of ten hours at 252 C. (McFadayen). 



One would suppose a priori that at a temperature so low that the protoplasm 

 becomes rigid, life must be temporarily suspended. According to the experi- 

 ment with the fish stated above this does not appear to be correct, for in this 

 case it would be a matter of indifference, so far as external signs go, whether 

 the temperature of a frozen fish were 15 or - 20 C., and yet after cooling 

 to 20 it dies. If life were actually suspended at 15 it would be difficult 

 to understand why a further lowering of the temperature has any effect. In 

 any case we may say that at these low temperatures life processes are reduced 

 to the minimum. 



If the chemical constitution or the temperature of the surrounding medium 

 be altered and the cells continue to live, various changes in their properties 

 may be induced, which, especially in the pathogenic microorganisms, are of 

 great importance, because the degree of their virulence may be thereby in- 

 creased or diminished (Pasteur). The protective inoculation introduced by 

 Pasteur is based upon these facts. 



After this general discussion we shall now proceed to the different mani- 

 festations of life, taking up in order the ingestion of food, digestion, the 

 oxidative processes, the elimination of decomposition products, the secretions, 

 and finally the phenomena of motility, production of light, formation of heat 

 and the generation of electricity. 



