expire are by no means synonymous terms, an ob- 

 servation long since made by Mayhow, who remark- 

 ed, that if air be drawn into the lungs, and the 

 mouth and nostrils afterwards closed, " quamvis in- 

 flati maneant pulmones, mori tamen necesse erit, 

 quia non licet expirare *. If indeed we reflect, that 

 during submersion in water no fresh air can enter 

 into the lungs, but that all which they contain may 

 freely escape ; and if we consider, that before sus- 

 pension by the neck in the human subject, a deep 

 inspiration, under the influence of fear, as Dr Good- 

 \vyn observes, is made, and that no air can after- 

 wards pass out, if the cord completely close up the 

 trachea; it is reasonable to expect, that this -varia- 

 tion in the bulk of air contained in the lungs should 

 obtain, under the very different circumstances in 

 which respiration is brought to a stand. 



91. How much the composition of the air itself, 

 and the manner in which it is breathed, will vary the 

 bulk of residual air in the lungs, we may collect 

 from the experiments of various authors. Dr Hales 

 moistened a bladder, and fixed to it a fosset, both 

 of which would contain 74 cubic inches of air. Ha- 

 ving blown up the bladder, he put the small end of 

 the fosset into his mouth, and, at the same time, 

 pinched his nostrils close, that no air might escape 

 through them, and he then breathed to and fro the 

 air contained in the bladder. In less than half a mi- 

 nute, he found a considerable difficulty of breathing, 

 and was forced after that to draw his breath very 



Tractat. Quinque, p. 300. 



