556 SAMUEL H. HURWITZ 



of much study. A thorough discussion of the present-day views concerning 

 this problem is given by Morawitz(c). As he points out, the suggestion 

 that a diminished oxygen supply to the bone-marrow may stimulate the 

 new formation of erythrocytes gains support mainly from the finding of 

 an abnormally large number of red 'blood-cells in conditions where there 

 is a lessened oxygen supply to the body, either through the inspired air, 

 as in high altitudes, or where there exists a difficulty in the absorption 

 of oxygen through the lungs, as in congenital heart disease. 



A critical examination of the evidence upon which this view is based 

 makes it certain, however, that diminished oxygen supply is not the only 

 stimulus which governs erythrogenesis. Oxygen deficiency, if present, 

 usually results in the formation of acid bodies in the blood which give 

 rise to a diminished carbon-dioxid tension in the alveolar air and a 

 diminished carbon-dioxid combining power of the blood. One would ex- 

 pect such indirect evidence of oxygen lack to exist in acute and chronic 

 anemias, where regeneration of blood-cells is going on actively. But 

 the newer methods of study have failed to demonstrate with any cer- 

 tainty the presence in these conditions of a diminished carbon-dioxid 

 tension in the alveolar air or a decrease in the carbon-dioxid combining 

 power of the blood (Morawitz(e) ). 



It has been suggested by Itami(a) (6) and by Ritz that in addition to 

 diminished oxygen supply, the products of erythrocytic disintegration may 

 furnish a normal stimulus to the bone-marrow. Support for such 

 an assumption comes from the active regeneration noted in anemias pro- 

 duced by hemolytic agents. Whether this stimulus is of the nature of a 

 lipoid derived from the hemolyzed red blood-cell (Kepinow) or a com- 

 plement-like substance contained in the serum (Carnot) is uncertain. 

 Morawitz and others are more inclined to the former view. 



Tests of Bone-Marrow Activity. So long as the number of cir- 

 culating erythrocytes remains constant, it may be assumed that a balance 

 exists between blood destruction and blood formation. But if the count 

 is rising or falling, it is difficult without special methods to estimate the 

 relative rate and degree of blood destruction and regeneration. The 

 value of urobilin estimations as a criterion of the rate of red cell dis- 

 integration will be discussed under hemoglobin metabolism. Some direct 

 knowledge concerning the rate of blood formation has come from the 

 application of vital staining to this problem. Besides a study by fixed 

 blood-smears of the erythroblasts, Howell-Jolly bodies, Cabot ring forms 

 and certain types of stippling as a means of estimating the effort required 

 of the blood-forming organs to maintain the cellular elements at a certain 

 optimum level, emphasis has been placed by recent workers (Pepper and 

 Peet, Lee, Minot, Sappington) upon reticulated cells, platelets, and mito- 

 chondria as signs of bone-marrow stimulation. 



By methods of vital staining (brilliant cresyl blue, pyronin-methyl- 



