The trials were aimed at raising levels of hemoglobin, the oxygen-carrying molecule in the blood, to levels beyond that needed merely to treat anemia, Dr. DeLap said.

In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen.

When inhaled, carbon monoxide is easily absorbed into the blood and displaces oxygen by combining with the blood's oxygen-carrying molecule, hemoglobin, and hanging onto it 240 times as tightly as oxygen.

Hemoglobin is the oxygen-carrying molecule in red blood cells, and a defective form of this substance, called sickle hemoglobin, is responsible for sickle cell disease.

Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide.

Cigarettes produce carbon monoxide, which, when inhaled, binds to the oxygen-carrying molecules in your body, depriving you of air.

The disease occurs when red blood cells contain an abnormal form of hemoglobin, the oxygen-carrying molecules in blood, which can cause them to stiffen and contort into jagged shapes that can block and damage vessels.

Hemopure's inventor, Dr. Carl Rausch, said the substitute was made by isolating and purifying hemoglobin from cow's blood, and stabilizing the oxygen-carrying molecules to prevent them from breaking down in the body.

"We started looking at other potential applications of oxygen-carrying molecules and stumbled upon the idea of food packaging," he said.

The blood consists of hemoglobin, the oxygen-carrying molecule in red blood cells, encapsulated in bubbles that have the consistency of Jell-O.