STUDY OP BLOOD 163 



If our nutrient tests are applied to the serum which 

 was poured from the bottle containing the clot they fur- 

 nish the following interesting results: 



First. They show it to be rich in proteid. 



Second. They indicate small amounts of fats and grape 

 sugar. 



Third. They show the presence of salts. 



Fourth. They show that starch is absent. 



Fifth. The serum gives a weak alkaline reaction. 



These results justify the following conclusions in regard 

 to the composition of blood plasma : 



First. The proteid tests show that the plasma contains 

 other proteid matter beside the fibrin, since that was 

 removed by the clotting, and that this proteid matter 

 does not coagulate like fibrin when the blood is removed 

 from the living body. 



Second. The small amount of grape sugar in circulation 

 at any time is what we should expect from our study of 

 the formation of glycogen in the liver (see p. 142), while 

 the small amount of fat present shows that most of the 

 fat poured into the blood by the lacteals does not enter 

 into the general circulation but is used up by the living 

 tissues. 



Third. The absence of starch is accounted for by the 

 fact that all the starch was changed by digestion into 

 grape sugar and enters the blood in that form. 



Fourth. The presence of salts explains the osmotic pres- 

 sure of the blood, accounts for its alkahne reaction, and 

 serves to keep certain proteids in solution. 



Finally, the presence of these particular nutrients shows 

 in an indisputable way that it is the plasma of the blood 

 which is the carrier of digested nutrients. 



