We know from the work of Holtzer, Marshall, & Finck (1957), who used a fluorescent antibody staining technique, that by the end of the second day of development in the chick (stage 13, Hamburger & Hamilton, 1951) myosin begins to be identifiable in the myoblast cells of the somites. We have no information so far, however, about the distribution of adenosine triphosphatase in the somites at this early stage, and one of the most characteristic properties of myosin (Engelhardt, 1946) is that it dephosphorylates adenosine triphosphate (ATP), a process which occurs during muscular contraction. The only studies of ATP-ase activity in developing chick muscle (Moog, 1947; Robinson, 1952) have dealt with stages from 12 days' incubation onwards, and have used muscle not all of somitic origin. In an earlier publication Moog & Steinbach (1945) included data on stages as young as 3 days, but used the whole embryo for assays of the enzyme activity.
Rapid Fluorescent-Antibody Staining Technique
