A bilaminar concept of the flow of blood through the peripheral vascular tree was foreshadowed by Coulter and Pappenheimer (1949). They say: '. . . in a two-phase system most of the energy required to maintain flow is dissipated in the peripheral sleeve, the axial core being carried along somewhat like the log in the centre of a stream.' They calculate from Newton's law of viscosity that the fraction of the cross-sectional area of tube occupied by the central core is not less than 0.85 at turbulence. This is not far from the figure of 1.0 predicted on the theory outlined here.
CONCLUSION
'For a long time to come it remains painfully obvious, at least to the conscientious surgeon, that every procedure . . . must be looked upon as more of an experiment than a therapeutic procedure. . . . It is obvious that the only reliable way to assess flow in a circulatory system is to measure it.' (Cannon and others, 1960.) In this paper are discussed indirect methods of assessing the flow of blood. Whether they are sufficiently sensitive to assist the surgeon in deciding how much reconstruction is needed, and, having carried out his reconstruction, whether the surgeon will be able to give a more accurate prognosis must be the subject of another study. The theory of bilaminar flow, however, helps explain some paradoxical findings in the renal (Lawrence, Doig, Knight, MacLaren, and Donald, 1964) and the carotid (Brice and others, 1964), besides the peripheral arteries.
SUMMARY
I n vitro and in vivo studies of blood-flow suggest I . Blood-flow can be visualized as occurring in two that :- concentric laminae.
ANTI-CANCER AGENTS
693 2. The relative dimensions of the laminae are related to the volume flow. 3. They are obtained from relating the crosssectional area of an artificial stenosis to its resultant pressure gradient; and therefore give an index of 4. The measurements can be obtained during an The mode of turbulence generation is discussed. I am most grateful to Professor G. W. Taylor and Mr. B. N. Catchpole for their interest; to the photographic department of St. Bartholomew's Hospital for their reproductions; and to Mr. Peter Cull for Fig. 11. Mr. M. P. Curwen derived the formula for calculating cross-sectional areas. blood-flow. operation for reconstructive surgery.