PHYSIOLOGY. 199 



itself, it is equally difficult to ascertain its proportion either to 

 the whole mass or to the several parts of it. 



" Upon the whole of this inquiry into the state of the blood, 

 with respect to its aggregation, or with respect to the state and 

 proportion of the several parts which compose it as an aggre- 

 gate, it seems not only to be uncertain how far these circum- 

 stances give a difference of temperament, but, on the contrary, 

 it seems probable, that they never do so in any considerable 

 degree. 



" Notwithstanding all this, ever since chemical reasonings 

 have been admitted into our physiology, that is, ever since the 

 time of Paracelsus, physicians have considered our fluids as 

 distinguished by the state of their chemical mixture, either in 

 the whole of the mass of blood, or in the several parts which 

 compose it as an heterogeneous aggregate. It is, however, in 

 the latter view only, that is, with respect to the several parts, 

 that we can chemically consider the subject ; and here it will 

 be readily acknowledged, that, till very lately, much frivolous, 

 hypothetical, and false reasoning has prevailed in the chemical 

 doctrines respecting the nature and state of our fluids. Even at 

 present, physicians have hardly come to be sufficiently chaste 

 in avoiding such hypothetical doctrines ; and however confident 

 they have been in their chemical reasonings, I am unable to 

 find any thing either clear or certain upon the subject. Not to 

 mention how little we have yet learned of the nature of vege- 

 table or animal substances from their chemical analysis, it is 

 enough to say here, that with respect to some parts of the mass 

 of blood, it is by no means ascertained either that their chemi- 

 cal mixture is upon different occasions anywise changed, or what 

 change is produced, or in what manner such change is effected. 

 This may be very confidently asserted with respect to the red 

 globules, the mechanical or chemical properties of which are 

 neither of them clearly ascertained ; and we neither know how 

 they are formed or produced, nor in what manner they may be 

 chemically changed. 



" I cannot dismiss this subject without observing, that the 

 supposition of a preternatural spissitude of the mass of blood, 

 or as it may be expressed of a lentor, being a frequent cause of 

 disease, has had a great share in almost all the modern systems 



