114 THE PHILOSOPHY 



greater or a lefs ; and this difFerent difpofitlon of bodies Is 

 called their capacity of containing abfolute heat. 



Do£lor Crawford next endeavours to prove by experi- 

 ments, that, when phlogifton is added to any body, its ca- 

 pacity of containing abfolute heat is diminifhed j and that, 

 when phlogifton is abftra^led from the fame body, its capaci- 

 ty of receiving abfolute heat is augmented. Hence he in- 

 fers, that heat and phlogifton feem to conftitute two oppo- 

 fite principles in nature. By the a6lion of heat upon bodies, 

 the force of their attraction to phlogifton is diminiftied ; 

 and, by the action of phlogifton, a part of the abfolute heat, 

 which exifts in every fubftance as an element, is expelled. 

 « Hence,' fays the Dodlor, ' animal heat feems to depend 

 « upon a procefs fimilar to a chemical elective attraction. 

 ' The air is received into the lungs, containing a great quan- 



< tity of abfolute heat. The blood is returned from the ex- 

 « tremities, highly impregnated with phlogifton. The at- 

 « traClion of the air to the phlogifton is greater than that of 

 ^ the blood. This principle will therefore leave the blood to 

 « combine with the air. By the addition of the phlogifton, 



* the air is obliged to depofit a part of its abfolute heat ; and, 

 « as the capacity of the blood is, at the fame moment, in- 

 ' creafed by the feparation of the phlogifton, it will inftantly 

 « unite with that portion of heat which had been detached 



* from the air. 



* We learn from DoClor Prieftley's experiments with ref- 



* pe(St to refpiration, that arterial blood has a ftrong attrac- 



* tion to phlogifton : It will, confequently, during the cir- 



* culation, imbibe this principle from thofe parts which re- 



< tain it with the leaft force, or from the putrefcent parts of 



* the fyftem : And hence the venous blood, when it returns 



* to the lungs, is found to be highly impregnated with phlog- 



< ifton. By this impregnation, its capacity for containing 



* heat is diminiftied. In proportion^ therefore, as the blood, 



