IN the address given by Sir Leonard Rogers to the Indian Science Congress at Bombay (NATURE, May 29) reference is made to the treatment of cholera by injections of saline solutions, with the object of replacing the fluid lost from the blood, which loss may amount to 67 per cent, of the plasma volume. The distinguished worker found that isotonic sodium chloride solution (0.85 per cent.) was practically useless, but that hypertonic solutions (1.2 per cent.) were of much greater value. Since the walls of the blood-vessels are freely permeable to salts, there is no permanent difference of osmotic pressure between their contents and the tissue spaces outside them. Hence there is no permanent force to prevent the escape of fluid from the blood-vessels. So long as the salt-content of the blood, as raised by the introduction of hypertonic solutions, exceeded that of the tissue fluids in his cases, there would be absorption of water and the blood-volume would be maintained; but before long the salt concentration of the tissues would rise to that of the blood, and there would no longer be the difference of osmotic pressure necessary to hold the fluid in the circulation against the filtration due to the arterial pressure. This would explain the repeated injections found necessary by Sir Leonard Rogers. In some experiments that I have made, 2 per cent, sodium chloride was found to leave the circulation and cause "dema, although not so rapidly as isotonic solutions did.