INFLUENCE OF HEAT AND COLD. 



bodies present originated spontaneously in a fluid 

 after it had been exposed to this high temperature. 

 In every instance in which living forms have been 

 attributed to spontaneous generation, the possibility 

 of their origin from germs cannot be denied or dis- 

 proved. 



We have yet very much to learn concerning the 

 influence both of high and low temperatures upon 

 the minute particles of bioplasm constituting the 

 germs of the lowest forms of life. And there is no 

 doubt that the effect of the same degree of tempera- 

 ture would be different at different phases of the life 

 of each species of fungus or low organism, and at 

 different periods of the year. The effect would also 

 vary according as the organisms were exposed to 

 sudden great alterations of temperature, or submitted 

 to intense cold or heat by slow and gradual changes ; 

 and even in man and the higher animals it is remark- 

 able what great degrees of heat and cold can be borne 

 if only the change be gradual. Some of the lower 

 forms of life are habitually exposed to a temperature 

 of 32, and would probably bear a very much lower 

 temperature without being destroyed. These crea- 

 tures, it must be remembered, are not merely exposed 

 externally to this temperature like many vertebrata 

 which have the power of developing heat within them- 

 selves, and whose temperature does not therefore vary 

 with that of the surrounding medium, but they suffer 

 every change which affects the medium in which they 



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