THE BOXES AND JOINTS. 745 



lymphocytes of normal blood (see page 376 ). But they are usually larger, 

 though varying much in size, have one large, often vesicular nucleus 

 staining less strongly than the lymphocyte nuclei, while the protoplasm 

 usually contains ueutrophile granules. These cells are called myelocytes 

 (page 380). In addition to these the marrow may contain, mingled with 

 its usual elements, nucleated red blood cells, spheroidal cells containing 

 red blood cells, and not infrequently considerable numbers of small 

 octahedral crystals (called Charcot's crystals). 



The degree to which this accumulation of cells occurs varies much in 

 different cases, and the gross appearances of the marrow are consequently 

 very diverse. In some cases the marrow is soft and has a uniform red 

 appearance, or it is variously mottled with gray and red. Occasionally 

 circumscribed haemorrhages are seen. In another class of cases, in which 

 the cell accumulation is more excessive, the marrow may be gray, 

 grayish-yellow, or puriform in appearance. 



These changes may occur in the central marrow cavity, as well as in 

 the marrow spaces of the spongy bone. They may be present in several 

 'or many of the bones. They are usually accompanied by analogous 

 changes in the spleen and lymph-nodes. 



In certain cases of acute and chronic anaemia, particularly in the perni- 

 cious and progressive varieties, the marrow, especially of the larger long 

 bones, may lose its yellow color from absorption of the fat, and become 

 red. Microscopical examination of the marrow under these conditions 

 may show myelocytes and sometimes, an abundance of developing nucle- 

 ated red blood cells and Charcot's crystals. 



In many of the acute infectious diseases, typhus and typhoid fever, 

 ulcerative endocarditis, recurrent fever, etc., the bone marrow has been 

 found hyperaemic, and may, it is asserted by Ehrlich, contain myelocj'tes 

 in increased numbers. 



All these lesions of the marrow, although our knowledge of them 

 is still very incomplete, together with what is known of the physiological 

 functions of the marrow, point to a close relationship between the mar- 

 row and the spleen and lymph- nodes as blood-producing organs. 



TUMORS. 



Tumors of the bone may involve either the periosteum, or the com- 

 pact bone, or the medulla ; or, as is more frequently the case, two or 

 more of these structures may be involved at once. Tumors of the bone 

 are usually accompanied by various secondary and sometimes very marked 

 alterations of the bone tissue, osteo-porosis, osteo- sclerosis, ossifying peri- 

 ostitis, etc. The new growths are very apt to undergo calcification and 

 ossification. 



Fibromata may grow from either the periosteum or the medulla. 

 Their most common seat is in the periosteum of the bones of the head and 

 face. They are apt to form polypoid tumors projecting into the posterior 

 nares, pharynx, mouth, and antrum of Highmore. Central fibromata, 



