THE MAST CELLS 



in this situation in the normal rat. A few tissue mast cells are always present 

 in the investing layer of periosteum which more closely resembles fibrous tissue 

 elsewhere. 



Many haematologists have observed, as a rare event, an increase in the 

 number of tissue mast cells in the bone marrow of man and have sought to 

 endow the finding with diagnostic or prognostic significance. Undritz (1946), 

 Leitner (1949) and Bremy (1950) record such an increase in cases of aplastic 

 anaemia; Messerschmitt (1954) found them regularly in the marrow of patients 

 suffering from chronic blood loss. Bremy (1950) concludes his monograph 

 with the suggestion that not only does an increase occur in patients with aplastic 

 anaemia, but also in cases of anaphylaxis, and that the chief underlying cause 

 is a reticulosis affecting the bone marrow. Both he and Fadem (1951) consider 

 the possibility that the mast cells are the cause of the depressed haemopoiesis. 

 However, Johnstone (1954), in a re-examination of the problem, failed to find 

 any significance, diagnostic or prognostic, in the occasional appearance of 

 tissue mast cells in the bone marrow of man, though he acknowledges that the 

 highest content seen by him was in a case of Banti's splenomegaly. Johnstone 

 makes the interesting observation that the tissue mast cells in the marrow 

 generally lie at the periphery of small nodules of lymphoid cells, much as they 

 are related to nodules of non-encapsulated lymphoid tissue in the gut wall of 

 cattle (p. 45) and to the 'milk spots' in the omentum of the rat (Webb, 1931). 

 It was noted earlier that tissue mast cells are not common in capsulated lymph 

 nodes (Holmgren, 1946). 



The writer is inclined to agree with Williams (1952) and de Vinals (1954) 

 that, in all probability, tissue mast cells in bone marrow have much the signifi- 

 cance that they have elsewhere, being a normal component of the connective 

 tissues (Riley, 1954). Hence, if the connective tissue framework of the bone is 

 proliferating, as in the reticuloses, or if the haemopoietic marrow is reduced, 

 as in aplastic anaemia, then local conditions favour an increase in tissue mast 

 cells. 



Two pathological conditions affecting the long bones of rats have recently 

 been described which support this view. In the first, a triple syndrome of 

 decalcification — rickets — osteitis fibrosa is associated with fibroplasia in the 

 metaphysis (Urist and MacLean, 1957). The second is the lathyrus syndrome 

 in which there is distortion and remodelling of the shaft (Gillman, 1958). 

 A mastocytosis develops in the zone of abnormal fibroplasia in each case. 





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