cmbryoiiic tissue, the periplieral hloocl. Antisera against the serum of adult cliickeiis were absorbed with yolk suspensions aiid tested quantitatively against extracts of blood from successive stages of development.
ACKNOWLEDGMEST
It is a pleasure to tliaiik Dr. Albert Tyler of the California Institute of Tecliiiology for his critical reading of this manuscript.
Methods
Zrijection aritigewr. Serum was collected from about 50 Ehode Island Red cliickeiis beiiig prepared for market. The &ole blood, obtained froin the neck veiiis aiid arteries, was pooled in wide-mouthed hfasoii j a r s and allowed to clot over night at rooni temperature. The serum was pipetted into 60 nil glass Centrifuge tubes, ceiitrifuged until clear at 3100 revolutions per miiiute in an Iiiternatioiial Clinical Centrifuge and stored over night at 4Β°C. The clear serum was passed through a Seitz filter, placed in P e t r i dishes in 25 ml aliquots, frozen, and desiccated to dryness iii Z'QCUO. The dry powder was stored in ICalin tubes at -10 to -15Β°C.
The injection antigen coiisisted of 3 portions of serum reconstituted a s 2% solutions by the addition of 1 ml sterile distilled water per 20 mg d r y serum.
Injectiom schedules, atztibody collection arid storage. The 2% solutioiis of reconstituted adult chicken serum were injected, on alternate days, into 3 rabbits (nos. 91, 103, and 104) of the Dutch breed. No. 91, which had been injected 7 moiitlis previously with adult chicken seruni, received the following' doses: 1.00 ml iiitraperitoncall;, 0.10, 0.20, 0.50 and 1.00 ml in the posterior marginal vein. A nioiitli later it received 0.50, 1.00 nil intraperitoneallp, 0.10, 0.25, 0.50 and 1.00 ml iiitraveiiously. The previously uniiijected rabbits (110s. 103 aiid 104) received injections of 0.25, 0.50 and 1.00 in1 intravenously * Obtained through the cooperation of Mr.