SURFACE TENSION OF SERUM : V. RELATION BETWEEN TIME-DROP AND SERUM ANTIBODIES.

An attempt was made to apply to the study of immune sera the fact, pointed out in our previous papers, that at a given dilution the serum shows a maximum drop of surface tension in function of time (time-drop). The results of the experiments here reported would seem to indicate that: 1. The time-drop of a serum solution is greater after the animal has been immunized than before immunization (from 50 to 100 per cent). 2. The time-drop is maximum at a dilution of 1:10,000, as had been predicted from the data previously acquired. 3. The size of the molecules or micellæ is probably unchanged after immunization, since the maximum drop is not shifted then. 4. Measurements made during the process of immunization showed that the time-drop increases after the 8th day and second injection, and reaches a maximum toward the 13th day, while the controls undergo no increase. 5. The injection of substances non-productive of antibodies, such as homologous cells or turpentine, does not result in the production of a permanent maximum. This shows that the maximum observed when heterologous cells are used is due to the presence of antibodies, and not to the mere injection of foreign material. 6. The measurement of the refractive index of the sera failed to demonstrate any differences between the sera of the controls and those of the experimental animals.