6 ANALYTIC SECT. II. 
converts, among whom was the celebrated Stahl, 
who supported it with all the weight of his 
authority, both as a professor and an author. It 
was not founded, like the preceding theory, on 
simple assertion, but had enough of reasoning in 
its support to give it a scientific appearance. Birds, 
said its advocates, respire a great quantity of air, 
and have a high animal temperature; fishes and 
reptiles respire little, and possess a low tempera- 
ture; while in man the heat augments with in- 
creased rapidity of the respiration, and vice versa. 
On these slender premises was founded the opi- 
nion, that animal heat is caused by respiration. 
The pneumatic theory met with few opponents ; 
it adapted itself with facility to the humoral 
pathology of the time; neither did it militate 
against the doctrine of autocrateia, for which 
Stahl and his followers were determined sticklers. 
On the discovery of oxygen, by Priestley and 
Lavoisier, there existed no disposition on their 
part to limit its influence; the former having 
shown, that it is the grand agent of combustion 
in general; and the product of respiration and 
combustion being the same, the probability there- 
fore was, that an evolution of caloric takes place 
in the lungs during respiration. 
111. Boerhaave had observed, that the agitation 
of atmospheric air with venal blood, changed its 
colour from a deep purple to a bright scarlet tint. 
a 

