108 ANIMALS AND VEGETABLES II. 
It remains to inquire how the exhalations of 
refpiration are noxious to animals: and here in 
particular has Sig. Cigna difplayed his abilities. 
According to him, they induce death by irrita- 
tion of the bronchie and lungs, forcing them to 
contract and corrugate, and thus prevent the ad- 
miffion of new air. ‘Thus, in his opinion, ani- 
mals in air infected by their breath die by fuf- 
focation. He endeavours to prove that this is 
actually the caufe of death, from the various 
fymptoms obferved in the refpiration of confined 
animals. Refpiration becomes more frequent 
and fainter when the exhalations begin to collect, 
becaufe an equal quantity of air infpired containing 
more, it obliges the animal immediately to dif. 
charge it. As they continue to increafe, refpira- 
tion alfo continues frequent, but becomes more 
laboured ; and foon exhaufts the animal if con 
fined in air where other animals have died. All 
this proves, in Cigna’s opinion, that the exhala: 
tions injure the animal, by contracting the organs 
of refpiration by their irritating influence, and 
thus obftru& admiffion of the air. 
In my numerous experiments, I have feen the 
fame fymptoms of injured refpiration. They 
are manifeft in warm blooded animals, and efpe- 
cially in birds. In cold blooded animals, they 
do not fo evidently appear, but are very percep- 
tible on changing animals from open to cenfined 
air 
