414 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



pressions in which special attributes of men are associated with the 

 nature and quality of their blood. One said of a nobleman or of a 

 criminal that it is "in his blood" ; of the calm and calculating that he is 

 "cold blooded"; of the well-born "blue blooded"; of the closeness of 

 family ties "blood is thicker than water." The scientific evidence, as 

 we shall see when we consider the viscosity of blood, is adequate to 

 prove the latter contention, but despite the great advances that have 

 recently been made, it is not yet possible to distinguish chemical attri- 

 butes of the blood which could form the basis for the other expressions, 

 residues of the folklore of blood. 



When Mephistopheles demands of Faust that he sign the compact 

 pledging his soul in blood, Goethe has Mephistopheles explain to the 

 protesting Faust that "blood is a juice of rarest quality." Goethe's 

 Faust appeared at the beginning of the nineteenth century. Mar- 

 lowe's Doctor Faustus goes less far in freeing blood of its biblical and 

 medieval mysteries by ascribing to it peculiar properties as a juice 

 or body fluid. 



The mysteries that have always been ascribed to the blood have 

 not been entirely solved by modern science. Blood performs more 

 functions than we have learned to ascribe to the substances in it that 

 we recognized. We now recognize many substances in the blood 

 whose functions are not yet understood. We may hope, however, 

 to resolve these mysteries by increasing our knowledge of this "juice 

 of rarest quality" which is the circulating fluid of the body. 



THE RED CELLS AND THE RESPIRATORY FUNCTION OF THE BLOOD 



This circulating fluid contains cellular elements of various kinds. 

 Most important among them are the erythrocytes or red cells and the 

 leukocytes or white cells. The red cells perform the respiratory func- 

 tion of the blood; the composition and functions of the white cells 

 are less well known but are generally associated with phagocytic 

 activity. 



The circulating blood is in equilibrium with all the tissues of the 

 body. Anatomists had explored the distribution of arteries, capil- 

 laries, and veins, and Harvey demonstrated the circulation of the 

 blood propelled by the heart through this complex system. Nine- 

 teenth-century physiology recognized and investigated the interchange 

 between the various tissues and the blood winch Claude Bernard 

 called the milieu interieur, or internal environment. Considered from 

 the point of view of respiration, the blood carries oxygen to the tissues 

 and removes carbon dioxide and other waste products from them. The 

 mechanism for oxygen transport is not only situated within the red 

 cells but can be associated with certain specific proteins that they 

 contain. 



