The existence of several values for the surface tension of urine has suggested the intervention of different substances in the determination of surface tension. We used the study of the changes induced in the three values of P obtained for a sample. Different repartition capacities were considered as corresponding to different groups of substances. Several methods were used in order to identify these substances. In one method, different constituents of the urine were separated by using solvents or absorbents, or by allowing the constituents to assemble at the surface.

The fact that the solvents, if they remain in the fluid even in very minute amounts, influence the surface tension, has largely handicapped their use. However, when lipid solvents were used and could be thoroughly eliminated, the treated urine showed a change in surface tension, especially in P1 values. With the use of activated animal charcoal absorption, all the P values were changed toward higher values.

M. Bier in our laboratories has studied the nature of the surface active constituents, separating them from urine by using the fact that they assemble at the surface. Urine was made to foam by passing an inert gas through it. The foam—and, with it, a high proportion of surface active substances was separated. By repeating the procedure, the separation could be pushed far enough so that it could be seen that the ST values, especially those of P3, were influenced. Analyses of the fractions obtained indicated that lipids would intervene in determining the surface tension revealed by the P1 value, while proteins would intervene for the P3, i.e., after a repartition requiring a specific time. We have tried to confirm these preliminary data by adding the agents to urine and following the changes induced.

The addition of minimal amounts of soaps to urine has been found to induce a change in all P values and especially in P1. The addition of billiar salts changed P2 values, while the addition of proteins, such as albumin, influenced the values of P3. It would appear from this preliminary research that while P1 changes are related to an increase in fatty acid derivatives, P2 changes are related more to the intervention of billiar acids, while proteins and amino acids exert greater influence on the values of P3.

This explains why surface tension, corresponding to P1, is still high in urines rich in albumin, and sometimes also in those with billiar acids. It would also explain the observation in the Hay's Test with sulfur flower in urine, that the sulfur starts to fall quickly if the urine is left standing for a while, but for the same urine this fall occurs only after a certain time if the sulfur is added to urine immediately after stirring. With surface tension affected by fatty acids even in minimal amounts, ST changes in relationship to conditions where these substances intervene are particularly interesting. It is chiefly with these data in mind that we tried to investigate surface tension in relation to normal and abnormal physiology.

Surface Tension And Normal And Abnormal Physiology

The ability to measure surface tension rapidly and accurately enough, even for very small amounts of fluid, has made it a preferred method for many investigations. In addition to clinical applications, where the information furnished has been especially valuable, we have utilized this method in experiments in animals.