88 EXTERNAL CONDITIONS OF VITAL ACTIVITY. 



130 or 140 per minute, so as to generate the greatest amount of heat 

 just before the young bees are liberated from the combs. In one in- 

 stance, the thermometer introduced among seven nursing-bees stood at 

 92 J; the temperature of the external air being 70. We observe in 

 this curious propensity a manifest provision for accelerating the deve- 

 lopment of the perfect Insect, which requires (as already pointed out) a 

 higher temperature than the larva, in virtue of its greater activity. The 

 Nurse-bees do not station themselves over the cells which are occupied 

 by the larvae ; nor do they incubate the nymph-cells with any degree of 

 constancy and regularity, until the process of development is approach- 

 ing its highest point. 



128. The influence of variations in the Heat of the body upon its 

 vital activity, is further manifested by the very remarkable experiments 

 of Dr. Edwards ; who has shown that Cold-blooded animals live much 

 faster (so to speak) at high temperatures, than at low; so that they die 

 much sooner, when deprived of other vital stimuli. Thus when Frogs 

 were confined in a limited quantity of water, and were not permitted to 

 come to the surface to breathe, it was found that the duration of their 

 lives was inversely proportional to the degree of heat of the fluid. Thus 

 when it was cooled down to the freezing-point, the frogs immersed in it 

 lived during from 367 to 498 minutes. At the temperature of 50, the 

 duration of their lives was from 350 to 375 minutes ; at 72, it was from 

 90 to 35 minutes ; at 90, from 12 to 32 minutes ; and at 108 death 

 was almost instantaneous. The prolongation of life at the lower tempe- 

 ratures was not due to torpidity, for the animals perform the functions of 

 voluntary motion, and enjoy the use of their senses ; but it is occasioned 

 by their diminished activity, which occasions a less demand for air. On 

 the other hand, the elevation of temperature increases the demand for 

 air, and causes speedier death when it is withheld ; by increasing the 

 general agility. The natural habits of these animals are in correspon- 

 dence with these facts. During the winter, the influence of a sufficient 

 amount of aerated water upon their exterior serves to maintain the re- 

 quired amount of respiration through the skin, so that they are not 

 obliged to come to the surface to take in air by the mouth. As the 

 season advances, however, their activity increases, a larger amount of 

 respiration is required, and the animals are obliged to come frequently 

 to the surface to breathe. During summer, the yet higher temperature 

 calls forth an increased energy and activity in all the vital functions ; 

 the respiration must be proportionably increased ; the action of the air 

 upon the cutaneous surface, as well as upon the lungs, is required ; and 

 if the animals are prevented from quitting the water to obtain this, they 

 die, as soon as the warmth of the season- becomes considerable. The 

 result of experiments on Fishes, in regard to the deprivation or limited 

 supply of the air contained in the water in which they are immersed, is 

 exactly similar ; the duration of life being inversely as the temperature. 

 And precisely the same has been ascertained with respect to hyberna- 

 ting Mammals ; which, as already remarked, are for a time reduced, 

 all such conditions, to the level of cold-blooded animals. 



129. The energy of the reparative actions of Animals is much influ- 

 enced by temperature, as might be inferred from what has been just 



