420 TEMPERATURE AND LIFE. 



clieraical action most thoroughly at 40°. At 20° it acts slightly, and at 

 60° its action ceases entirely. In considering the tissues of complex 

 organisms, we ascertain analogous phenomena. Protoplasms of dif- 

 ferent organisms, although they are often supposed to be identical, 

 present very unequal opposition to thermic variations. In one case it 

 dies at 30° or 20°, in others it lives at 0°, at — 5°, at —10° (Norden- 

 skiold). We know that eggs of birds require for their development a 

 temperature, narrow in limits, which can not be overstepped without 

 destroying the embryo, or producing malformations. Eggs of inverte- 

 brates are somewhat similar, but their exigencies are less restricted, 

 and they accommodate themselv^es to greater differences of temperature. 



Every being, to live and move, requires environment of a certain 

 temperature. Some are less exacting, and adapt themselves to varia- 

 tions; others, on the contrary, can not endure even slight changes. 

 Some seek the cold, others — heat; but all in a marked manner, as we 

 know from the difficulties experienced in acclimating species to a new 

 climate. A few examples will not be out of place. The polar region, 

 with its prolonged and rigorous cold, and our high summits, always 

 clothed with a mantle of ice, produce a fauna and flora which is peculiar 

 to them. In these regions, wdiere man is able to exist only at the cost 

 of a considerable effort, there are mammals, insects, plants of all kinds, 

 which can reach here only their full growth and perfect development. 

 In a temperate or warm climate they lose their vitality and perish, 

 never in reality becoming acclimated. Warm-blooded animals which 

 live in these regions have the same temperature as their co-species in 

 warm climates. They maintain themselves by appropriate food and 

 a heavy growth of fur, discarded by them when the weather moderates. 

 Captain Black has observed in Siberia when the external temperature 

 was at —35°, that the temperature of a fox was 41°, making a difference 

 of 76°. The reverse of these polar regions and glaciers are the hot 

 springs. Here also we find a characteristic fauna and flora. Many 

 observers have drawn up a list of sea weeds, infusorials, and fungi, 

 living in the waters, the temperature of which varies from 50°, 00°, and 

 even 00° C, and that thrive and multiply. 



Between the coldest regions, which some species delight in, and the 

 hot springs, or the tropical regions, where others attain their highest 

 development, we find grades of organisms whose resistance to extremes 

 of temperature is less and which prefer more temperate surroundings, 

 manifesting a partiality for such and such a point in the thermic scale. 

 To be assured of these preferences one has only to consult the docu- 

 ments showing the distribution of species and their acclimation. The 

 most curious fact disclosed by the preceeding data is the great resist- 

 ance of the protoplasm of certain creatures to temperatures, which, 

 judging from other cases, one would suppose must be fatal. The pro- 

 toplasm in certain cases can sustain a temperature of zero, or lower 

 still, and others can live at 90° and even higher temperatures. This is 



