The bone-marrow as a blood-forming structure is intimately concerned in diseases in which the constitution of the blood is altered. Most of these conditions have been already considered under Pernicious anaemia and Leukaemia. They consist chiefly in a transformation of the yellow marrow in the situations where it occurs either into a red marrow such as occupies the medullary spaces in the foetus, or into a white or yellow lymphoid marrow whose structure resembles that of lymphatic glands (see under Leukaemia). With this transformation there is sometimes atrophy of the bony lamellae so as to give more space for the accommodation of the altered marrow.
Besides these lesions, the bone-marrow is liable to lesions in acute infective diseases, these lesions somewhat resembling those of the spleen. There is hyperaemia and there are sometimes haemorrhages which may take the form of infarctions. According to Golgi, the bone-marrow in haemorrhagic small-pox shows everywhere diffuse haemorrhages.
In old age the adipose tissue of the marrow is liable to undergo diminution, and its place is taken by a Gelatinous substance which is sparely cellular.
Neumann, Arch d. Heilk., x. and xi., Centralb. f. d. med. Wissensch., 1882, p. 321; Golgi, Rev. clin. di Bologna, 1873; Ponfick, Virch. Arch., lvi., lx.; Chiari (Small-pox), Ziegler's Beitrage, xiii.; Geelmuyden (Historical account and literature as well as independent observations), Virch. Arch., cv., p. 136.