The sour hams examined were obtained from four different packing establishments. All of the hams studied were “sweet-pickle hams” which had not been smoked. The sour hams selected for examination were good typical body sours, in which the sour odor was well developed, but not of the very pronounced or putrefactive type. The sour odor in every case was found to be more pronounced next to the bone, being usually rather more pronounced just behind the bone, that is, on the fat side of the bone. The sour odor in each instance was confined to an area of meat immediately surrounding the femur and extending out through the body of the ham for a variable distance, as shown by the dotted lines in figure 1, but in no case did the sour odor extend all the way to the margin of the meat, nor did it as a rule extend below the tibio-femoral articulation, the shank proper and the bone marrow of the shank (i. e., of the tibia) being usually sweet. The butt portion of the hams—that portion above and behind the hitch bone (symphasis pubis)—was also sweet. Immediately after sectioning, the sour areas, as a rule, could be readily distinguished by a difference in color. In the freshly cut hams the muscular tissue near the bone, where the sour odor was more pronounced, exhibited a slight but distinct grayish hue, at times having a slight greenish tinge; in other words, the muscular tissue in the sour areas lacked the normal bright red color of the sound meat and was distinctly lighter in color than the surrounding tissues. Upon exposure to air, however, the lighter, grayish, sour areas tend to assume a reddish hue and become much less pronounced than in the freshly cut ham. After the cut surface of the ham has been exposed to the air for some time it may be difficult to distinguish the sour areas by any difference in color. [Illustration: BUL. 132, BUREAU OF ANIMAL INDUSTRY, U. S. DEPT. OF AGRICULTURE. PLATE I. FIG. 1.—SECTION OF MUSCULAR TISSUE FROM SOUND HAM, SHOWING MUSCLE FIBERS CUT LONGITUDINALLY; NUCLEI SHARPLY DEFINED AND CROSS STRIATION DISTINCT. (Pen-and-ink drawing made with camera lucida from section stained with hematoxylin and eosin to show histological structure. × 320.)] FIG. 2.—SECTION OF MUSCULAR TISSUE FROM SOUR HAM, SHOWING MUSCLE FIBERS CUT LONGITUDINALLY; NUCLEI UNDERGOING DISINTEGRATION AND CROSS STRIATION INDISTINCT. (Pen-and-ink drawing made with camera lucida from section stained with hematoxylin and eosin to show histological structure. × 320.)] [Illustration: BUL. 132, BUREAU OF ANIMAL INDUSTRY, U. S. DEPT. OF AGRICULTURE. PLATE II. FIG. 1.—SECTION THROUGH MUSCULAR TISSUE OF HAM WHICH HAS UNDERGONE NATURAL OR SPONTANEOUS SOURING, SHOWING DISTRIBUTION OF BACILLI BETWEEN THE MUSCLE FIBERS, WHICH ARE CUT OBLIQUELY. THE DARK MASSES BETWEEN THE MUSCLE FIBERS REPRESENT CLUMPS OF BACILLI.