The concept of the hypertonicity of tears originated with Massart1 in 1889. By instilling various solutions of different osmotic pressure into the eye, he determined by subjective responses that the concentration of a solution which produces the least discomfort corresponded to a 1.4 per cent solution of NaCl. Massart's results were accepted readily and were included in the major pharmacopeias and textbooks.
In 1930 Ridley2,3 measured the osmotic pressure of tears of 3 persons by the depression of the freezing point and found the osmotic pressure of tears to be slightly below that of human blood.
Krogh4 used a modification of the Baldes5 vapor-pressure method for the determination of osmotic pressure. Krogh, Lund, and Pedersen-Bjergaard6 found the osmotic pressures of 10 samples of tears equal to those in solutions of from 0.87 to 0.92 per cent NaCl.
Schaeffer,7 using a capillary-tube method, estimated the