This is a thesis issued by the Eugenio Ruiz Memorial Commission of the University of Chile. It includes discussions of the index of refraction, the protein content and the volume and quantity of red cells in the blood of 33 children under 1 year of age with dehydration. Tables of the results are given. The most noteworthy deviation from the normal was the increase in the content of protein in the blood. In 5 instances in which the level of protein was reduced, edema was present.