Blood volume studies in healthy children.

Among the earliest recorded experiments on the tion of the blood volume are those of Bischoff (1856, 1858) and Weicker (1858), who by exsanguinationm directly the amount of blood obtained from the bodies of executed criminals. Since that time much genuity has been xrcised in devising methods of esimating blood volume which would conbine accuracy with ease of application to the living human subject. The moder techniques involving the use of dyes owe their origin to the woirk of Keith et al. in 1915, and are in the writer's opinion the most pactical of all the methods. These techniques have undergone several modifications, the two most important being the substitution of a blue for a red dye and the adoption of the photoelectric absorptiometer for comparison of colours. The blue dye (Evans blue, or T1824) now m common use, is more slowly excreted than the red dyes, such as vital rd and congo red (Dawson ct aL, 1920), and, what is probably more important, does not mask the occurrence of haemolysis. Indeed the Evans blue method used in these studies not only permits the detection of haemolysis but allows for its correction. The photoeltric absorptiometer elminates the personal factor involved in colour matching Of recent years much information has been gained regrding the change in the volume of plasma and blood in such states as shock, debydration, and anaemia. Most of the investigations, however, have bee carried out in adults, and comparatively little work has been done in children, where the technical difficulty of venepunctur is greater. It is evident that any-study of changes in the blood volume in children and their application to disease must depend on the establishment of a normal range of values. This range will possess wide limits, since the blood volume is constantly changing with growth. It was considered necessary, therefore, as a preliminary procedure, to define the average volumes and the range at various ages as accurately