158 M. Dutrochet on the 



Sphynx Atropos, 24 hours after assum- 

 ing the perfect form, . . * . . r.04 F. (0.58 C.) 



The latter is the highest degree of vital heat which I have 

 observed among insects. 



These observations shew, that the vital heat of animals, with 

 a low temperature, is generally tery much inferior to what had 

 been previously assigned them, for it is found that, at its maxi- 

 mum, it does not reach 1°.08 of Fahrenheit. 



On taking a general glance at living beings with a low tem- 

 perature, whether vegetable or animal, it is seen that their 

 vital heat is in relation with the activity of their respiration, 

 and also with the physical condition of the respired air. It is 

 almost always appreciable in animals which respire elastic air ; 

 there is no exception to this heat in the gasteropodous mollus- 

 ca, whose lungs are very small, and seldom renew the air which 

 they contain. With regard to animals which respire air un- 

 der water by means of gills, their vital heat is so low, that it 

 does not manifest itself, even by employing the most delicate 

 thermo-electrical instruments. It is allowable to suppose that 

 this want of appreciable vital heat, is owing to oxygen in the 

 water, when it becomes fixed in the act of branchial respira- 

 tion, giving out only a small quantity of caloric comparatively 

 to what it yields when fixed by the act of pulmonary respira- 

 tion, or by that of tracheal respiration which is peculiar to 

 insects. 



Vegetables likewise respire elastic air, by respiratory or- 

 gans, in a state of high development, and, moreover, it is not 

 atmospheric air which they introduce into their organs, but 

 the oxygen gas disengaged by their green parts under the 

 influence of light. Their vital heat, therefore, ought to be at 

 least equal and sometimes higher than that of certain insects 

 or reptiles. This is what I have observed, and not without sur- 

 prise. Is it not, in fact, surprising that a plant, EupJiorbia 

 lathyris^ for example, should have a vital heat, which, at its 

 maximum, is ten times greater than that of a frog, and infi- 

 nitely greater than those of fishes, and all other animals that 

 breathe by gills l The family of Aroides, among plants, has a 

 vital heat in the spadix of their flowers, of so high a tempera- 



