BLOOD. 227 



contain six ounces of blood, this blood must be retained in them 

 for at least two minutes. This period is much shorter than 

 those deduced by Keil and Wagner, in which it amounts to 

 hours. 



I think we may fairly conclude, from the preceding ob- 

 sen^ations, that the changes which the blood undergoes in its 

 composition while passing through the kidneys and liver, are 

 appreciable ; for if we have shown the probabihty of the cor- 

 rectness of the statement in the case of the kidneys, there can 

 be no question that it is true in the case of the liver, which is 

 everywhere permeated by the torpidly circulating blood of the 

 vena portse. 



On the absolute composition of healthy venous blood. 



It cannot be doubted but that the blood of different indivi- 

 duals in a state of perfect health will exhibit differences of com- 

 position, and that it would be the merest chance if the compo- 

 sition of the blood of two persons were found to be precisely 

 the same. The circumstances capable of inducing a change in 

 the composition of the blood are very numerous. Different 

 methods of hfe, and various modes of nourishment, might cause 

 such changes; but, independently of these external influences, 

 there are others connected with the individual which must mo- 

 dify, to a greater or lesser degree, the composition of the blood, 

 as, for instance, the influences of sex, age, and temperament. 



It is extremely difficult to determine a formula for the com- 

 position of normal blood that would serve as a standard, by 

 comparison with which we might detect absolute deviations in 

 other forms and specimens of blood, on account of the variable 

 nature of the fluid, changing even in the same individual at 

 different periods of the day, and in accordance with the food 

 that has been taken. 



In a medical point of ^iew, the composition of venous blood 

 is the most interesting, because it is from the veins that blood 

 is almost always taken in disease, and because venous blood 

 can naturally only be compared with venous blood for the pur- 

 pose of ascertaining any deviations that may occur. 



Before attempting to give a decided opinion on the normal 

 composition of venous blood, it would be requisite that nume- 

 rous accm'ate analyses of the blood of healthy males and females 



