376 Royal Society : — 



by letters. I will therefore call the operation of simply bleeding once, 

 and then injecting, by the letter u ; that of repeated bleedings and 

 repeated injections by the letter w ; and that of cross-circulation by 

 the letter x. 



In none of these operations did I use any chemical means to de- 

 termine the degree to which the blood was changed ; for I did not 

 venture to compromise my chances of success by so severe a mea- 

 sure ; but I adopted the following method of calculation instead : — 



I calculate the change of blood effected by transfusion, or by cross- 

 circulation, upon moderate suppositions as to the three following 

 matters : — 



O) The quantity of blood in a rabbit of known weight. 



(2) The time which elapses before each unit of incoming blood is 

 well mixed up with that already in the animal's body. 



(3) The time occupied by the flow, through either carotid, of a 

 volume of blood equal to the whole contents of the circulation. 



As regards 1, the quantit\ of blood in an animal's body does not 

 admit, by any known method, of being accurately determined. I 

 am content to take the modern rough estimate, that it amounts to one- 

 tenth of its total weight. If any should consider this too little, and 

 prefer the largest estimate, viz. that in Valentin's 'Repertorium,' 

 vol. iii. (1838), p. 281, where it is given for a rabbit as one part in 

 every 6'2 of the entire weight, he will find the part of my argument 

 which is based on transfusion to be weakened, but not overthrown, 

 while that which relies on cross-circulation is not sensibly affected. 



As regards 2, the actual conditions are exceedingly complex ; but 

 we may evade their difficulty by adopting a limiting value. It is 

 clear that when only a brief interval elapses before each unit of newly 

 infused blood is mixed with that already in circulation, the quality of 

 the blood which, at tlie moment of infusion into one of the cut ends 

 of the artery or vein, is flowing out of the other, will be more 

 alienized than if the interval were longer. It follows that the blood 

 of the two animals will intermix more slowly when the interval is 

 brief than when it is long. Now I ])ropose to adopt an extreme 

 suj)position, and to consider them to mix instantaneously. The re- 

 sults I shall thereby obtain will necessarily be less favourable to 

 change than the reality, and will protect me from the charge of ex- 

 aggerating the completeness of intermixture. 



As regards 3, I estimate the flow of blood through either carotid 

 to be such that the volume which passes through it in ten minutes 

 equals the whole vohmie of blood in the body. This is a liberal esti- 

 mate ; but I could afford to make it twice or even thrice as liberal, 

 witiiout j)rejudice to my conclusions. 



Upon the foregoing data the following Table has been constructed. 

 The formulae are: — Let the blood in the Silver-grey be called a, 

 and let its volume be V, and let tlie quantity ?i of alien blood be 

 thrown in at each injection, then the quantity of blood u remaining 

 lu tlic Silver-grey's circulation, after u injections, 



-•('-vT 



