Training of Surgeons

SIR,-The article by Dr. A. E. Gent and his colleagues (2 November, p. 294) is of great interest. A minor criticism, both of this and of much other work on urine cell excretion, is that the authors assume that the small cells in the urine which are not derived from polymorphs originate in the renal tubules. The authors do not describe these cells, but since staining is necessary to distinguish them they are presumably of much the same size as polymorphs. Yet examination of a histological section of the kidney shows that the majority of renal tubular cells are much larger than this. It is true that such small cells can be obtained by scraping the cut surface of the kidney,' but under these circumstances contamination with blood is unavoidable, however much the surface is first washed with saline. Some work which I have done" suggests that many of these small cells are in fact lymphocytes or mononuclear cells. Cells from the renal tubules can be obtained by microdissection, and when suspended in saline or urine show a cytoplasm which stains in an irregular fashion with methylene blue, as well as hyaline droplet formation. The presence of lymphocytes and monocytes in the urine was known to workers in the earlier part of this century, but appears recently to have been overlooked.4 The practical consequences of this is that an increase in the numbers of small round cells in the urine should not necessarily be taken as evidence of damage to the tubules. A further point which should be given prominence by authors who work with the stain devised by Prescott and Brodie' is that its main constituent is metabolized in the body to a carcinogen.5-I am, etc.,