AMOUNT OF BLOOD. 219 



tained by washing out the blood vessels. Here the error arises 

 from the fact that, in washing out the blood vessels, 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 

 estimated ; thereupon a known quantity of water is injected into 

 the vessels. After some time being allowed for proper distribu- 

 tion of the water, a sample of the diluted blood is taken and its 

 solids estimated. 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 meas- 

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

 permanent and equally bright red color. It was then diluted 

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

 The blood vessels 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 to- 

 gether 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 correspond 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 : 



