From the point of view of pathologic classification as well as from that of clinical differentiation, the group of diseases that Mallory collectively designated by the term lymphoblastoma is still rather confusing. Pathologists do not have any difficulty in recognizing typical examples, but sometimes the pathologic features are far from characteristic, and absolute differentiation may be difficult or impossible. As far as Hodgkin's disease and lymphosarcoma are concerned, the clinician can seldom distinguish one condition from the other, but must depend on the pathologist.
It is now clear that these conditions are much more common than they were formerly thought to be. The etiologic factors are still obscure. Certainly, the attempt to incriminate the bacillus of tuberculosis or some other micro-organism has not been successful. In any large series of cases a background of tuberculosis can be found in a certain percentage, but in the majority tuberculosis does not appear