Morphology of lymphatic cells and of their derived tumours.

The morphological description of diseases of the lymphatic and reticulum cells, and the classification of neoplasms derived from these cells, are in a state of some confusionwhich arises, in part at least, from the different approaches and terminology used by histo- pathologists and by cytologically orientated haema- tologists. The addition of electron microscopy, of enzyme histochemistry, and of immunological methods for cell typing has not entirely resolved the differences. The subject is still in a state of rapid development but an analysis of current knowledge is needed to promote mutual understanding among histopathologists, haematologists, immunologists, and many others who may be concerned. Whereas attempts to classify neoplastic disorders of the haemo- poietic system have largely succeeded because the derivation of the tumour cells from the normal cells could be inferred from morphological study of marrow and blood cells, we have had to wait much longer for a comparable classification of lymphoreticular neoplasms-with the possible exception of Hodgkin's disease.