1. Bayer, quoted by Katz, “Animals and Men. Studies in Comparative Psychology” (Longman, Green and Co., London, 1937).
2. Welty, Physiol. Zool., 7, 85 (1934).
3. Harlow, J. Genetic Psychol., 41, 211 (1932).
4. Harlow, J. Comp. Psychol., 16, 171 (1933).
5. Cushnie and White, Vet. Record, 60, 105 (1948).