When the dye is injected continuously throughout the period of cyanide absorption a still greater fraction of the cyanide is bound in the blood. of subcutaneously administered cyanide is demonstrably bound in the circulating erythrocytes of dogs injected with methylene blue immediately before administration of the cyanide.

In vivo formation of methemoglobin is readily demonstrable after administration of both cyanide and methylene blue because of the stability of the cyanmethemoglobin which is formed. The failure of methemoglobin to accumulate is explicable on the basis of the known behavior of the reactions involved, namely, the reduction of the formed methemoglobin by leuco-methylene blue and the enzyme systems present in the erythrocytes, and the rapid disappearance of the injected dye from the blood.

This fact, however, should not bring into question the proposed methemoglobin explanation of the dye's action in cyanide poisoning. Methemoglobin does not accumulate in significant quantities in the blood of dogs after intravenous injection of clinically recommended quantities of methylene blue.

Cyanide poisoning methylene blue