1. Barr, D. P., G. G. Reader and C. H. Wheeler: Ann. intern. Med. 32, 6 (1950).
2. Baumgartner, W.: Schweiz. med. Wschr. 85, 1157 (1955).
3. Bock, H. E.: Verh. dtsch. Ges. inn. Med. 63, 292 (1957).
4. Burnet, F. M.: The clonal selection theory of immunity. Nashville 1958.
5. Centanni, E.: Zbl. Bakt. 43, 508 (1907).