38 BIOLOGY: GENERAL AND MEDICAL 



which the protoplasmic basis of the cells is kept moist 

 and soft, protoplasmic currents established, and the 

 molecular interchanges constituting metabolism made 

 possible. If low temperature transform the water to ice, 

 or if high temperature drive it off in the form of vapor, 

 life must either cease or become inactive until the essen- 

 tial conditions are restored. 



Freezing results in disintegration of the protoplasm; 

 high temperatures, in coagulation of the delicate sub- 

 stance. Active vital manifestations are thus only pos- 

 sible within limits marking the vital endurance of the 

 organisms observed. 



A striking difference in temperature relations charac- 

 terizes the active and passive states of living matter. 

 Thus many plants are killed by frost, whose seeds are 

 not injured by any known degree of cold; bacteria that 

 are killed at 60 C., may, in the spore stage, resist expo- 

 sure to 120 C. for a few minutes. This assumption of 

 the latent or passive form subserves the useful purpose 

 of enabling the animal to escape the rigors of winter, the 

 excessive dry heat of the desert, and other temporarily 

 unfavorable conditions. 



Different kinds of organisms show striking differences 

 in regard to temperature endurance. In general terms 

 this bears a direct relation to the developmental com- 

 plexity of the organism. The lowest forms of life some- 

 times show a temperature endurance ranging over 350 

 C.; the highest forms may not survive an actual change of 

 body temperature amounting to more than 5 C. 



Thus, the spores of certain bacilli may be exposed for 

 an hour to the temperature of liquid hydrogen ( - 225 C.) 

 and yet survive. When the temperature is slowly ele- 

 vated, and the spores are watched, it is found that no 

 change occurs until 6 C. is reached when an occasional 

 spore germinates and a bacillus emerges. As the tempera- 

 ture ascends, such of these bacilli as have survived are 

 found to be dividing, at first only at long intervals, then 

 with increasing frequency until when 12.5 C. is reached, 



