OP RESPIRATION. 397 



acid given off. And the more perfectly developed respiring animals 

 are, the less are they enabled to deprive atmospheric air of its whole 

 contents of oxygen : before its complete consumption they appear 

 languid, and, as it were, apoplectic, and they die upon the con- 

 tinuance of this state, or if they have not a fresh supply of air. 

 Whereas many insects, particularly butterflies, as animals upon a 

 lower grade of organisation, so entirely consume the oxygen in the air, 

 that in many experiments that have been made, not the hundredth 

 portion of that gas has been found left in it*. But the loss which 

 the air suffers by the withdrawal of the larger quantity of oxygen, in 

 lieu of which but one half the quantity of carbonic acid is given back 

 to it, appears to be replaced by a second excretion, consisting of azote. 

 One portion of this azote is given off by the lungs or air tubes, and 

 another portion, especially, by the perspiration of the skin. But as this 

 perspiration can be but trifling through the hard integument of insects, 

 if it be not indeed wholly deficient, they consequently must produce 

 less azote but a proportionably greater quantity of carbonic acid. 



These are the chief results of the experiments upon the respiration 

 of insects. In proof of them we will give a tabular view of other 

 experiments of Treviranus, without adding more recent ones of our 

 own, occasioned by our less familiarity with such experiments, and 

 from our deficiency in the necessary auxiliaries and instruments. 

 And indeed the results of the experiments of so experienced and 

 competent an observer may well suffice. 



* Sorg, pp. 65, 67. 



