The C.O.B. test has been carried out at 15 min. intervals on raw milk samples stored at 20°C. to examine worker and replicate variability. Within experimental limitations, the differences between workers were not significant (P>0·05) and, in general, good agreement was found between the five replicates examined for each milk sample, coefficients of variation less than 4·0%. The change from absence to presence of a precipitate generally occurred with successive tests, but there were indications that the times to increased intensity of clotting differed with samples.

Captain H. Barkworth was responsible for the plan and design of these experiments which were carried out by members of his staff at Shardlow.