120 PROTOZOA AND DISEASE 



periosteal sarcoma, when it is possible, calls for amputation far 

 above the disease, whilst a slow-growing central sarcoma is now 

 often treated by scraping away the sarcoma tissue, and allowing the 

 cavity thus produced to fill by granulation. When they are incised 

 also, the tumours differ in naked-eye appearance, the periosteal 

 sarcoma being of a pinkish-white colour at its superficial portion, 

 whilst ossifying spicules project into its substance from the surface of 

 the bone in which it has its origin ; the central sarcoma is usually 

 crossed by bands of fibrous tissue, which give it a tougher consistence 

 than has the periosteal sarcoma. It is often covered by a fibrous 

 capsule, and contains cysts which contain serous fluid. This type 

 of tumour is termed a ' myeloid sarcoma.' Histologicallyboth tumours 

 consist chiefly of myeloid tissue, the basis alike of the periosteal and 

 endosteal structure of bone. The multinucleated cells known as 

 myeloplaxes occur in both tumours side by side with uninucleated 

 cells, but the myeloplaxes are more abundant in the ' myeloid ' 

 tumour. The ordinary type of marrow-cell in a periosteal sarcoma 

 is shown in Fig. 48 large nuclei rich in chromatin and having a very 

 close nuclear network. Some of the cells in the superficial part of 

 the tumour are in process of subdivision, showing that there is a 

 numerical increase of tissue-cells in this form of sarcoma. The 

 tissue of the more active superficial part of the tumour is traversed 

 by blood-channels, the walls of which are built up of the adjacent 

 marrow-cells. In the periosteal sarcoma the parasites are numerous, 

 and show a striking contrast both to the marrow-cells and to the 

 blood-corpuscles. 



The earliest stage of the parasites that I have been able to detect 

 is a small non-nucleated body in the cytoplasm. In the larger forms 

 a nucleus may appear, as in Fig. 48 ; 7,2, and 4, but not infrequently 

 the bodies break up whilst still in the chromidial state (Fig. 48; J). 

 The close similarity of many of these bodies both to the nucleated 

 and the non-nucleated forms of the protozoa of cystic ureteritis is 

 very striking. Some of the cell-inclusions in some of these tumours 

 of bone are coarsely reticulated (Fig. 45). 



I need not dwell in great detail on the particular features of 



