vn] of the Seventeenth Century. 197 



He then goes on to ask the question why death follows 

 suppression of breathing. 



" Life, unless I mistake, consists in the distribution of 

 11 animal spirits, for the supply of which the beating of the 

 " heart and the flow of blood to the brain are absolutely necessary. 

 " And breathing seems especially to assist the beat of the heart, 

 " in a manner elsewhere described. Now it is very probable 

 " that this aereal salt is wholly necessary for all muscular move- 

 " ment, so that without it the beat of the heart cannot take 

 "place. For we have reason to think that the sudden con- 

 " traction of a muscle is due to particles of two different kinds 

 " mixing with each other, and mutually acting upon each other. 

 " Now we cannot suppose that both kinds of particles, the 

 " effervescence of which gives rise to the contraction of muscles, 

 " can come from the mass of the blood, for liquids which are 

 "derived from the same source unite again without any 

 " effervescence. So 'that it seems that something extraneous 

 " is requisite for bringing about the ebullition which leads to 

 " muscular movement. 



"We may therefore suppose that the nitro-saline particles 

 " derived from the inspired air supply the one class of motive 

 " particles which, meeting with the other, salino-sulphureous 

 ' particles furnished by the mass of the blood, but dwelling in 

 " the motor structures, excite that effervescence which gives 

 "rise to the muscular contraction, as we have fully shewn else- 

 " where. 



" The movement of the heart is carried out in the same way 

 "as in other muscles. 



" Hence, when breathing is stopped, since that aereal salt, 

 " needful for all movement, is lacking, the beat of the heart and 

 " therefore the flow of blood to the brain, are interrupted, and 

 "death necessarily follows." 



This view of the use of the nitro-aereal particles naturally 

 leads to the corollary that "breathing is increased during violent 

 ' exercise, not in order that a greater flow of blood may take 

 "place freely through the lungs, but in order to provide for 

 " the greater expenditure of the nitro-aereal salts in the many 

 " effervescences taking place in the contractions of the muscles." 



