BLOOD AND BLOOD DERIVATIVES — COHN 427 



The number of such globulins is far larger than our present physico- 

 chemical criteria for their characterization. Moreover, certain of them 

 appear to be present in very small amounts — amounts, however, ade- 

 quate to perform their natural functions. In diseases in which there 

 is a deficiency of any of these proteins, however, it would appear to 

 be of the utmost value to have them available, separated from the 

 plasma and concentrated as specific therapeutic agents. 



The blood of man is rich in lipid as well as in protein material. Only 

 a small amount of this lipid is present in an emulsified state ; most of 

 it is held in solution in more or less labile combination with the 

 various plasma proteins. Among the lipids that are readily dis- 

 tinguished are cholesterol, carotenoids, phosphatides, and cerebrosides. 

 Of these the carotenoids are found concentrated with certain ^-glob- 

 ulins in Fraction III (see table 2) which is also rich in cholesterol. 

 Cholesterol, phosphatides, and cerebrosides have also been found con- 

 centrated with a-globulins in Fraction IV. Here our study of plasma 

 proteins is leading us to a study of the plasma lipids, not as organic 

 chemicals separated from blood by methods which destroy the structure 

 of the lipo-proteins but in the state in which they exist in nature. 

 Their separation and purification as protein complexes should make 

 possible investigation of their function and an increasing understand- 

 ing of their role in the economy of the body. 



The economy of the body is controlled by a group of messengers, 

 hormones, secreted and liberated by various glands. These hormones 

 also find their way into the blood stream and some of them have been 

 identified, although they are present in but very small amount. Among 

 them is the thyrotropic hormone which appears to be closely related to 

 that secreted by the anterior pituitary gland. The gonadotropic hor- 

 mones secreted by this gland have also been identified in one or another 

 plasma fraction. As our survey of the hormones in the blood expands 

 it should be possible not only to concentrate and recognize more of 

 them but also to make them available as concentrates should they prove 

 to have any value in therapy. Their human origin should make it pos- 

 sible to use hormones derived from man when those derived from 

 animals lead to sensitization following repeated injection. 



The economy of the body is aided also by a series of enzymes whose 

 specific function it is to accelerate chemical reactions. The blood 

 stream contains many such enzymes. A cholinesterase and phos- 

 phatase clearly have functions related to the cerebrosides and phos- 

 phatides of the blood stream. Phosphatides of more than one kind 

 have been recognized both within and without the red cell. There are 

 lipases and proteolytic enzymes and the number of these is not yet 

 clearly defined. One, the fibrinolytic enzyme, will serve to illustrate 

 a principle that applies to others. The blood stream carries not only 



