Blood groups in sheep.

The A reagent: The A reagent (Table 1 ) was an unabsorbed, isoimmune antiserum. It was produced in a sheep named A, which received five intrajugular injections, at five-day intervals, of 5 ml of citrated blood from a sheep named B. The antiserum was collected five days after the last injection. Sheep A was of blood-group R in the R 0 system, and a preimmunization sample of her serum contained neither natural hemolysins nor agglutinins for the red cells of other sheep. Immune hemolysins were first demonstrated in the sample of serum collected just prior to the fifth or last injection. The antiserum, coded S3, was collected five days later. This antiserum had a uniform titer of 1/128 in tests with the reactive bloods of different sheep, suggesting that it might contain a single, nonfractionable population of antibodies in tests with the red cells of sheep. Numerous absorptions were performed in which bloods from individual sheep were utilized, and in each instance the reactive bloods exhausted all of the hemolysins. The S3 antiserum was used routinely at a dilution of $& as the A reagent of this study. At this dilution regular and complete hemolysis was usually effected within one and one half hours after the tests were set up. A rare exception to the observation of complete hemolysis with this reagent occurred in tests of the red cells of a pair of twins, and in that instance it was possible to show that the incomplete hemo-