subject of the foregoing Memoir. 35 



It is not my wish or intention to argue upon differences of 

 result between my own observations and those of previous 

 experimenters, but merely to refer to one or two points con- 

 tained in my paper, in order to prevent the occurrence of 

 such misconceptions as some of my friends have already fallen 

 into with respect to my views. 



In the first place, then, I do not consider the serum or any 

 part of the blood to contain an alkaline carbonate, but only to 

 yield such salt by incineration. My theory for the production 

 of the arterial tint has no reference to the decomposition of a 

 carbonate in the venous blood, but to the production of the 

 phosphate of soda, by the decomposition of animal organic 

 salts. 



Secondly, the analyses which have been made of arterial 

 and venous blood, showing identity, or nearly so, of the ash 

 obtained, are in no way opposed to my observations; for the 

 reason that, when the whole blood {clot and serum) is incine- 

 rated, the process of ignition does just what respiration would 

 do, and produces phosphoric acid from the phosphorized fats 

 of the venous blood-corpuscles. The difference between the 

 two kinds of blood is shown by the incineration of the serum 

 only of the two kinds of blood ; for then no corpuscles are 

 present to afford phosphorus to the venous serum for the pro- 

 duction of phosphoric acid. 



I took great care, when making my comparative experi- 

 ments, to guard against all fallacy which might arise from 

 resolution of precipitates by excess either of acid or ammonia, 

 &c. in testing with the silver salt. It is an experiment which 

 I have been much accustomed to make when examining animal 

 matters, and with the uses and peculiarities of which I have 

 been long familiarized. 



The very marked degree of difference which I have detected 

 between venous and arterial serum, leads me to believe that 

 the quantity of blood circulating is far less than is generally 

 supposed. 



It is much to be regretted that we have as yet no correct 

 means of ascertaining this interesting point, and that it is 

 scarcely possible, in the present state of our knowledge, even 

 to propose a plan which is not replete with practical difficulties 

 and theoretical objections. 



Believe me to be, my dear Mr. Phillips, 



Yours most truly, 



G. Owen Rees. 



D2 



