(\\it11 3 flgores in the text.)Vital injections differ from total injections of blood vessels in that Itith the former the injection mass mixes with the blood and is distributed by the heart as the blood is distributed. It therefore shows the number of vessels in use, rather than the number in existence. R : 7 such a method one may study quantitative changes in the vascularity of organs and tissues not suitable for microscopic inspection in vivo, or in which an exposure of the part is a distortion of physiological conditions. Obviously if the method is delicate enough to indicate physiological variations it is applicable also for the study of pharmacological and pathological changes in the number of vessels open.The ideal substance for such vital injections should be physiologically inert, that is a) it should not be poisonous to the animal, b) it should not agglutinate, c) nor should it cause the blood to coagulate within the vessels, d) it should not diffuse through the capillary walls: e) the volume necessary to render the capillaries visible should be small enough not to induce plethora. f) it should not be soluble in the clearing agents used for microscopic preparations, g) if in addition the substance is chemically stable and does not occur in the body naturally, quantitative chemical estimations of vascularity map become possible.A number of substances were tested from these points of view, but found to be unsatisfactory. The list includes soluble starch, potassium ferrocyanide and iron ammonium citrate. and the vital dyes brilliant Der Redaktion am 1. Sovember 1929 zugegangen. 5 *

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