THE BLOOD 217 



The Quantity of the Blood. This cannot be estimated 

 by measuring the blood escaping from the opened vessels 

 of an animal, for much will fail to come out. The residual 

 blood may be washed out and the dilution of the mixture 

 estimated. It will then be possible to calculate the 

 original total. Earlier estimates of the blood in the 

 full-grown human body placed the volume at 5 quarts 

 or liters. The recent tendency is to lower figures, 

 4 liters or 9 pounds being a reasonable assumption. 



Plasma and Corpuscles. We may call blood a red 

 fluid but the color is due to microscopic bodies suspended 

 in a liquid which is, by itself, nearly colorless. The 

 liquid basis is best called the plasma. The suspended 

 particles are the " formed elements" or corpuscles. It 

 is convenient to call them cells, though the majority of 

 them do not come up to the standard in all respects. 

 If we give them this rank we can look upon blood as a 

 tissue, the intercellular substance being fluid instead 

 of solid. 



The plasma constitutes something more than half 

 the volume of human blood. Considering that the 

 corpuscles fill about 40 per cent, of the space in any mass 

 of blood we may well wonder at its free-flowing properties 

 The solid bodies must be both smooth and elastic to 

 permit such perfect fluidity. The corpuscles are defi- 

 nitely denser than the 'plasma and in some cases they may 

 subside in a tall vessel until there is a clear layer of 

 plasma at the top from which samples can be drawn. 



Blood plasma is a highly complex solution. The most 

 abundant of the compounds in it are the proteins. The 

 plural is used with sufficient reason for there is no doubt 

 that three kinds of protein are present if not a larger 

 number. The significance of these proteins is obscure. 

 Not long ago they were thought to be formed continually 

 in the cells lining the intestine and consumed as food by 

 the tissues in general. But the view is gaining acceptance 

 that they are a rather stable and permanent mass, little 

 subject to depletion and so requiring but little renewal. 



