The results obtained in this investigation are admittedly not as extensive as is desirable but they allow certain conclusions to be drawn.
1. The sodium and potassium contents of the body fluid of Ascaris lumbricoides are somewhat variable, but these variations do not seem to be dependent upon those of the external medium.
2. The calcium and magnesium contents of the body fluid are relatively constant and are not affected by those of the external medium.
3. The chloride concentration of the body fluid is closely related to and always remains lower than that of the external medium.
4. As shown in Table 2, there is a large gap between the total concentrations of inorganic cations and anions in the intestinal fluid of the pig. Presumably a considerable proportion of the inorganic cations are combined with organic anions, at present undetermined. Exposing the worms to saline media composed of chloride caused a large rise in the internal chloride concentration. This may well be a limiting factor in the life of the animals in such media, and the next step forward would seem to be the fuller analysis of the environment to which they are normally exposed.