Surface Tension of Serum

As stated in previous papers, 1-4 the four essential conditions under which the presence of antibodies in immune serum can be detected and followed by means of what might be termed the tensiometric method are: first, the dilution of the serum to 1:10,000; second, the use of strictly clean vessels; third, the care in handling the solutions, which must absolutely not be disturbed between the two measurements; and fourth, the study of the time-drop, 2 and not merely of the initial value of the surface tension. The first condition is a consequence of the numerous experiments reported in Papers I, 1 II, ~ IV, a and V. * The second has been emphasized in the same papers, and will be referred to again in the present paper. The third condition is satisfactorily fulfilled by the device represented in Fig. 1. However, the main object of this paper is to explain more extensively the reason of the fourth condition. 1. Time-Drop and Initial Value.--The results of a series of ten experiments on rabbits are reported in Text-fig. 1. From its mere inspection, it will be clear that the values of the initiaa surface tension of the solution of immune serum (1 part in volume of serum to 10,000 parts of saline 0.9 per cent) are sometimes higher and some-