IMPORTANT FOODSTUFFS, IMPORTANT TISSUES 123 



They can move about, can reproduce, and have other functions 

 characteristic of living cells generally. 



The red corpuscles are living but contain no nuclei in mam- 

 mals. There are from 5-6 millions per cubic millimeter in nor- 

 mal blood, but they may fall to one-half that number in certain 

 diseased conditions. 



The platelets are structures derived probably from the white 

 corpuscles, possibly also from the red. They play an important 

 role in the clotting of the blood. It has been reported that they 

 contain nuclein, but this has been contradicted. 



The chief plasma proteins are serum albumin, one or more 

 serum globulins and fibrinogen. 



The blood contains various enzymes in small amounts, e.g. 

 amylase (acts on glycogen), a glycolytic enzyme (acts on glu- 

 cose), lipase, proteolytic enzymes and an invertase, the amount 

 of which is increased if cane sugar is injected or fed in large 

 amounts. 



A reaction which has attracted much attention in the last few 

 years is known as the Abderhalden reaction. This investigator 

 found that if a foreign protein is injected into the blood, 

 enzymes appear which have the power of breaking down the 

 albumoses produced by digesting that protein with cold H 2 SO 4 

 for 24 hours. The serum of a pregnant woman will digest an 

 albumose-peptone mixture obtained from placental tissue in 

 this way. The digestion of the materialcan be followed by ob- 

 serving the slight change in optical activity of the mixture, or 

 by dialyzing off the amino acids produced and confirming their 

 presence by the ninhydrin test. There is some difference of 

 opinion as to the value and reliability of this test for the diag- 

 nosis of pregnancy. 



Reaction of the Blood. The blood is almost neutral it is 

 alkaline to litmus and acid to phenolphthalein. Nevertheless, 

 much acid must be added to blood before any great change in 

 its reaction is produced. This is due to the fact that it contains 

 NaHCO,, Na 2 C0 3 and Na 2 HP0 4 , and alkali salts of the blood 

 proteins. Any strong acid will form its sodium salts, taking the 



