1. Fry, C. S., and Wilkinson, A. E. (1963). Brit. J. vener. Dis., 39, 190.
2. Wilkinson, A. E., and Rayner, C. F. A. (1966). Ibid., 42, 8.
3. The simple measurement of the optical density of a specimen at a characteristic absorption band for oxyhaemoglobin does not give satisfactory results because of the presence of bilirubin and small quantities of other pigments. However, when optical density measurements need to be made in the presence of a background level of other absorbing materials it is possible to correct for the non-specific light absorption in a manner which has been described by,1950
4. MATERIALS sions centrifuged at 500 r.p.m. for five minutes at 4°C. The packed cells were washed once in the growth medium and centrifuged again before resuspending them in a minimal amount of the growth medium. The liver cells were subsequently cultured after implantation by the method of Zuckerman, Tsiquaye,1967
5. Nagington, J., and Lawrence, M. F. (1962). Mth. Bull. Minist. Hlth. Lab. Serv., 21, 162.