212 MANUAL OF PHYSIOLOGY. 



tained by washing out the bloodvessels. Here the error arises 

 from the fact that, in washing out the bloodvessels, much solid 

 matter besides that belonging to the blood is taken from the 

 tissues and thus an excess is found. 



Valentine's Method. A small quantity of blood is drawn from 

 a vein and measured and its percentage of solids is accurately es- 

 timated ; thereupon a known quantity of water is injected into the 

 vessels. After some time being allowed for proper distribution of 

 the water a sample of the diluted blood is taken and its solids es- 

 timated. The difference in solid contents of the two samples 

 shows the degree of dilution caused by a known quantity of water 

 introduced into blood of ascertained strength, and thus the amount 

 of the fluid diluted (the blood) may be calculated and added to 

 the amount of the first sample of blood. 



This method cannot give accurate results, because in the time 

 necessary for the distribution and mixture of the water with the 

 circulating blood much of the former is excreted by the kidneys 

 and skin, and the second sample of blood is more concentrated 

 than should result from such dilution. 



Welcker's Method depends upon the estimation of the coloring 

 matter of the blood. He connected the carotid with a small T 

 piece, and allowed the animal to bleed into a bottle in which the 

 blood could be defibrinated by shaking with pieces of glass. One 

 cubic centimetre of this defibrinated blood was carefully measured 

 off and saturated with carbon monoxide (CO), which gives a per- 

 manent and equally bright red color. In was then diluted with 

 500 c.c. distilled water and kept as a standard color-solution. The 

 bloodvessels of the animal were then washed out with .6 per cent, 

 solution of sodium chloride until the solution flowing from the 

 jugular vein was colorless. The tissues of the animal were then 

 chopped up and steeped in water and pressed. The washings of 

 the vessels and the infusion from the tissues were added together 

 and diluted until they had the same color-intensity as a layer of 

 the standard solution of the same thickness. Every 500 c.c. of 

 these diluted washings corresponds to 1 c.c. of blood. 



By this method the following estimates have been made of the 

 relation of the blood to the body weight : 



