The purpose of this paper is to describe the histological appearance of tissues from the dystrophic calves reported by Blaxter, Watts & Wood (1952), to compare the dystrophic lesions with those found in naturally occurring muscular dystrophy of cattle (Hjarre & Lilleengen, 1936a, b, Vawter & Records, 1947Slagsvold, 1925), and to relate the chemical composition of the muscle to its histological appearance. METHODSAs described in a previous paper (Blaxter et al. 1952), four experimental groups of calves were involved; two receiving cod-liver oil as a source of vitamin A and D activity and two a solution of pure vitamins A and D in arachis oil. Vitamin E was given to animals in one of each of these groups, the other group receiving none. The calves are referred to by treatment and replication number as previously described.Blocks of muscle were fixed with 5 % formaldehyde or 5 % formol saline. Sections were stained by Mayer's haemalum and 5 % aqueous eosin. Gallego's method (see Langeron, 1949) was used to demonstrate connective tissue. Sections were also stained with phosphotungstic acid and haematoxylin. Table I summarizes the results of the examination of skeletal and cardiac musculature, together with details of the macroscopic appearance of the muscle and its chemical composition. Both normal muscles from normal animals and 'normal' muscles from dystrophic animals were included in this study. RESULTSThe agreement of the results was on the whole good. Muscle classified as normal macroscopically and containing the usual quantities of dry matter, total nitrogen and creatine was found to be normal when examined histologically. There were, however, several discrepancies. The flabby heart of calf no. CL0.E. I , although containing subnormal amounts of creatine, was histologically normal, and the semimembranosus of calf no. CL0.E. 4, though of normal composition and appearance, nevertheless showed an increased number of nuclei. These discrepancies are partly due to the sampling errors involved when a small piece of muscle is excised for histo-

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