1. Intravenous injections in rabbits of F. Weber Co.'s Drawing Ink gave the following results:

(a) With large doses, an outpouring of nucleated red blood cells, in many instances reaching high values (60,000 to 70,000 per c.mm.), accompanied by a slight initial rise of erythrocytes and hemoglobin, followed by a moderate anemia and in one animal, a severe anemia.

(b) With smaller doses the presence of nucleated red cells in the peripheral blood was correspondingly less, the hemoglobin and erythrocytes increasing above the initial level. This increase was sustained for a considerable time, followed by a decrease to or below the initial level.

(c) Pregnancy caused a marked suppression, and, shortly before delivery, a complete suppression of the normoblastosis. Nucleated red blood cells reappeared in the blood after the litter was cast.

2. The filtrate of Weber's Drawing Ink, obtained through a Berkefeld filter W, produced the same effects, somewhat enhanced, as the whole ink.

3. The bone marrow of the animals injected with Weber's ink and the filtrate, both showed a marked erythrocytic hyperplasia, with many open sinuses lined with nucleated red blood cells in all stages of maturation.

4. As the dialysed ink gave practically the same results, and the dialysate proved to be without any effect, the conclusion was drawn that a non-dialysable protective colloid was responsible for the marked stimulation of the hematopoietic organs.

5. The delivery of nucleated erythrocytes was interpreted as due to growth pressure induced by rapidly growing red blood cells as well as intrasinusoidal formation of erythrocytes. Pressure due to rapidly increasing phagocytic cells must also be considered.

6. It is fair to conclude that carbon particles as such stimulate endothelial cells mainly toward clasmatocyte formation without incapacitating the endothelial cells, while colloidal silver apparently had a toxic and incapacitating effect on this system of cells.

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