1. Carbon monoxide, 0.5-13%, is found in the float gases of Physalia. Oxygen comprises 15-20% of the total gas. Carbon dioxide is present in negligible amounts.
2. The gas gland, pneumadena, is the site of carbon monoxide formation.
3. L-Serine is the substrate for carbon monoxide formation.
4. A strikingly large concentration of folic acid is found in the gas gland.
5. It is suggested that carbon monoxide secretion serves to inflate the float of Physalia and that carbon monoxide is later slowly replaced by air through diffusion and exchange.