1. M. W. Darlington andP. L. Mcginley, Department of Materials Report, March 1974, to be published.
2. M. W. Darlington, P. L. Mcginley andG. R. Smith, to be published.
3. A. Engstrom, in ?Physical Techniques in Biological Research?, Vol. 3, edited by G. Oster and A. W. Pollister (Academic Press, New York, 1956) p. 495.
4. C. G. Waterfield andJ. Peacock,S.P.E. Tech. Papers 19 (1973) 393.