275 
the most correct experiments which had then been 
made, but was supported by the whole range of ana- 
logical facts, presented in the vegetation of plants, 
and in the respiration of the inferior . animals ; and 
it is a conclusion of such great importance, in con- 
ducting us towards a true explanation of the respira- 
tory function, that we shall not hesitate again to re- 
cite, very briefly, the evidence adduced in its support, 
together with such additional facts and arguments, 
as subsequent researches have enabled us to collect 
and bring forward. 
564. Among his earliest experiments relating to 
respiration, Dr Priestley found, that if a mouse was 
confined in a jar of air, inverted in mercury, until he 
died, no diminution in the bulk of air took place, but 
the residual air lost nearly one-fifth of its bulk, when 
shaken with water * ; facts which entitle us to infer, 
that no portion of the air was absolutely lost, but 
that the whole of its oxygen was changed into an 
equal bulk of carbonic acid. Similar results, as we 
before remarked (83.), were obtained by Dr Craw- 
ford, who also observed no diminution to attend the 
respiration of air inverted over mercury, but the re- 
sidual air afterwards lost one-fifth of its bulk by agi- 
tation with solution of potassa. Dr Menzies, in his 
experiments on respiration, found no diminution to 
occur in the volume of air respired ; and therefore 
necessarily inferred that the bulk of acid formed was 
equal to that of oxygen gas which disappeared t 
* Phil. Trans, an. 1772. 
f Dissert, on Respirat. p. 50. 
