THE BLOOD. 549 



As soon as they are formed, they are given up by the cells to the blood 

 and immediately leave the body. Such substances are urea, uric acid, 

 creatine, hippuric acid, and conjugated glucuronic acids, all of which we 

 may in a sense regard as end-products of metabolism. Blood-serum is 

 never perfectly colorless. It always has a yellow tint, the color being 

 ascribed to a certain dyestuff, called lutein. Its chemical nature is 

 wholly unexplained. Serum always contains inorganic constituents, and 

 the amount appears to be very constant. It would be highly interesting 

 to have definite knowledge concerning the distribution of the inorganic 

 substances, and above all concerning the way they are combined in the 

 blood, plasma, and serum. Unfortunately, there are no known methods 

 for giving us such information. At present we are forced to rely upon the 

 chemical examination of the ash, the results of which naturally have but 

 a relative value. In this way we are able to ascertain what constituents 

 are present in the ash, but we obtain absolutely no information as to how 

 the phosphoric acid, for example, is combined in the blood or plasma. 

 This phosphoric acid may arise from inorganic phosphates, or from organic 

 phosphorus compounds, such as lecithin, nucleic acid, etc. The value of 

 an ash analysis can be increased by attempting to determine in what dif- 

 ferent way the respective amounts of the constituents may have been 

 combined. It would be, of course, likewise desirable to obtain by physico- 

 chemical methods some idea as to the content of the blood and of the 

 plasma in electrolytes and non-electrolytes. As the most important 

 result of physico-chemical investigation of the blood, we will mention the 

 highly interesting observations of Hoeber * that the concentration of the 

 hydroxyl ions in blood-serum and in the blood is almost exactly the same 

 as that of distilled water. Both liquids are from this point of view to be 

 considered as neutral. 



Blood always contains cells, namely, the red and white corpuscles. 

 Whereas the latter are to be regarded as true cells, the former are, in man 

 and mammals, not to be considered as perfect cell-structures. Only in 

 the beginning of their development do they possess a nucleus, which they 

 lose as soon as they become active in the blood. The red corpuscles of 

 birds, reptiles, amphibia, and fishes do, however, contain nuclei. In spite 

 of extensive investigations but little is known concerning the chemical 

 construction of the red corpuscles. It is true that we know fairly well 

 what components are present, but we do not understand how they are 

 combined. The red corpuscles do not possess any true membrane. It 

 has been assumed that they consist of stroma filled with liquid. 2 They are 



1 Pfliiger's Arch. 81, 522 (1900). G<za Farkas: Mathematikai s termSszettudo- 

 manyi e~rtesito, 21, Vol. 1 (1902). P. Fraenkel: Pfliiger's Arch. 96, 601 (1903). 



2 H. J. Hamburger: Osmotischer Druck und lonenlehre in den medizinischen Wis- 

 senschaften, Wiesbaden, 1902. Cf. Rollett: Pfliiger's Arch. 82, 199 (1900). 



