RHEOLOGICAL STUDIES OF NEW CREAM BASES 233 speeds employed in the Brookfield and, for instance, the Epprecht rheomat, where the speed change is by a jerk as it were. In the Ferranti Shirley there is a continuous speed range. I would like your comments on the possible significance of this. It seems to me that the Ferranti Shirley, in particular, makes a very good colloid mill, and the measurement is not on the product that one first started measuring. This appears to point in fayour of the Brook field where, at any rate the surface area of the spindle is not very great. On the other hand, the criticized Helipath device ensures that emulsification is kept to a minimum. Do you not think that this is a point in fayour of its use ? THE L •CTUR•R: I think that at the lower speeds of 1 and 0.5 rpm the spindle is revolving so slowly through the material that the torque is much higher at the low rates of shear, and therefore the measurements are incorrect. There is a varying pressure on the material and you therefore have a side effect which cannot be measured accurately. The instrument must be suitable for measurements of Newtontan and pseudo-plastic fluids but not for plastic thixotropic material.

Book reviews THE BIOCHEMISTRY OF THE NUCLEIC ACIDS. 5th Edn. J. N. Davidson. Pp. xv q- 352 q- Ill. (1965). Methuen • Co., Ltd., London. 35s. U.K. only. The first edition of Professor Davidson's book appeared in 1950. The appear- ance of this, the fifth edition, after only 15 years is a measure, not only of the popularity of the book, but of the tremendous progress made in the study of the chemistry and functions of nucleic acids over this period. It is, of course, a topic of compelling interest to everyone, and there can be few chemists and biologists who do not wish to be at least acquainted with current developments in the field. The book is intended to provide an elementary outline of the main features of the nucleic acids and nucleoproteins for the benefit of students of biochemistry, of chemists who wish to know something about the biological aspects of the subject, and of biologists who wish to learn a little about the chemical aspects. It falls naturally into two halves, which may be said to be the static and dynamic aspects of the subject respectively. Commencing with a description of hydrolysis products and chromatographic behaviour, the first half continues with the preparation, structure and properties of RBIA and DBIA, a discussion of nucleases and related enzymes, and proceeds through chemical methods of estimation and histochemistry to a discussion of nucleic acids in viruses. In the second half are the chapters of more dramatic interest, being a discussion of the biosyntheses of DBIA and RNA, and a description of their functional involvement in transfer of genetic information and in protein synthesis. Coverage of the whole field of nucleic acid biochemistry is completed with chapters on biosynthesis and catabolism of the nucleotides. Professor Davidson states that the book has become known in his laboratory as "The Child's Guide to the Blucleic Acids." This is legitimate comment only in so far as the book is lucidly written and is easily read by the non-specialist. The information contained is nevertheless detailed and comprehensive, and is up to date to January 1965. Each chapter contains a long list of references for further reading, and the book possesses a good index. It is to be thoroughly recommended for anyone wishing an introduction to, or a refresher course on, the subject. There remains one small point of criticism. The two-page list of abbreviations at the beginning of the book does not include all the abbreviations used in the text, and the occasional searching back through a chapter to find a definition can be a minor irritation. B.G. OVERELL. 235