THE GENERAL CONDITIONS OF LIFE 291 



a farther sinking of the temperature should still be of influence. 

 For the present, therefore, we must forgo a definitive solution of 

 this question. 



The establishment of the maximum of external temperature 

 meets with difiiculties similar to those surrounding that of the 

 minimum. In every case the maximum is represented by the 

 point where the proteids in the living substance of the cell 

 coagulate. The proteids play in the life of the cell the most 

 essential role, and it is conceivable that, when the dissolved 

 albumin passes over into the solid state, metabolism, in other 

 words life, must cease. Accordingly, it might appear very simple 

 to determine the maximum of temperature at which life can still 

 exist. But the temperature of coagulation is very different for 

 different proteids, and, moreover, there are kinds of organisms 

 that still live even at temperatures at which all proteids must 

 long since have coagulated. 



In a similar manner as with the minimum, Kuhne ('64) per- 

 formed experiments upon Ammba regarding the maximum of 

 temperature, and found that, when creeping actively at ordinary 

 temperatures, it contracted at 35° C, but still remained capable 

 of life ; after being heated to 40° — 45° C. it could not be revived by 

 cooling. Thus, Kiihne was able to establish that one proteid of 

 the amoeba-cell, which he regarded as contractile substance, 

 coagulated at 40° C, another at 45° C. For plant-cells Max 

 Schultze ('63) found the death-point to be at 47° C. In 

 contrast to these, various other authors have given accounts of 

 remarkable cases in which organisms exist at much higher tem- 

 peratures. The most remarkable testimony was the observation 

 of Ehrenberg ('58), who found living ciliate Inftosoria and 

 Rotifera between the threads of Oscillaria in the hot springs of 

 Ischia at a temperature of 81° — 85° C. Hoppe-Seyler ('77), who 

 tested this statement of Ehrenberg at Casamicciola, Ischia, 

 found considerably lower temperatures. Ahja\ when exposed to 

 hot vapours, were living at 64-7° C, but, when in water, the 

 highest temperature in which they existed was only 53° C. Hence 

 it is certain that organisms are still able to live in water of 53° C. 



Some time ago very detailed investigations were under- 

 taken in the hot springs of the Yellowstone Park in North 

 America, and living algjE were found at much higher tempera- 

 tures. The older statement of Ehrenberg does not appear 

 therefore, to have been incorrect. 



Although these statements are surprising, a well-authen- 

 ticated and easily observed fact is known that is much more 

 remarkable. This is the behaviour of the spores of certain 

 bacteria to high temperatures. Koch, Brefeld and others, have 

 shown that the spores of the bacillus of splenic fever {Bacillus 

 anthracis) and the hay-bacillus (Bacillus suUilis) can endure 



u 2 



