242 The Rise of the Modern [lect. 



" Respiration and putrefaction affect common air in the same 

 " manner, and in the same manner in which all noxious processes 

 " diminish air and make it noxious, and which agree in nothing 

 "but the emission of phlogiston. If this be the case it should 

 " seem that the phlogiston which we take in with our aliment, 

 " after having discharged its proper function in the animal system 

 "(by which it probably undergoes some unknown alteration) 

 "is discharged as effete by the lungs into the great common 

 "menstruum, the atmosphere." 



He saw, moreover, in the changes of the colour of blood 

 a confirmation of his views. Venous blood he took to be 

 blood laden with phlogiston ; this reaching the lungs parted 

 with its phlogiston to the dephlogisticated part of the inspired 

 air in the lungs, and went on its way as dephlogisticated blood 

 to gather up phlogiston once more as it coursed through the 

 body. A proof of this view he saw in the fact that blood 

 exposed to dephlogisticated air gave up its phlogiston and 

 became bright arterial dephlogisticated blood. Arterial blood 

 exposed to phlogisticated air became phlogisticated, dark, and 

 venous. 



11 Having taken the blood of a sheep I introduced pieces 



" of the crassamentum, contained in nets of open gauze, 

 " sometimes through water, and sometimes through quicksilver, 

 "into different kinds of air, and always found that the blackest 

 " part assumed a florid red colour in common air, and more espe- 

 " cially in dephlogisticated air, which is purer and more fit for 

 " respiration than common air (and accordingly the blood always 

 "acquired a more florid colour, and the change was produced 

 " in less time in this than in common air); whereas the brightest 

 " red blood became presently black in any kind of air that was 

 " unfit for respiration, as in fixed air, inflammable air, nitrous 

 "air or phlogisticated air; and after having become black in 

 " the last of these kinds of air, it regained its red colour upon 

 " being again exposed to common air or to dephlogisticated air ; 

 " the same pieces becoming alternately black and red, by being 

 " transferred from phlogisticated to dephlogisticated air ; and 

 "vice versa. 



" In these experiments the blood must have parted with its 



