124 PROTOZOA AND DISEASE 



difference between the infiltration of a tissue by sarcoma and an 

 inflammatory formation such as tubercle.' 1 



The facts and comments given above show, I think, that this dis- 

 tinction is not an absolute one. The alveolar sarcoma of the breast is 

 an instance of an infective granuloma caused by protozoa, and it is as 

 simple and direct as any other infective granuloma, a passage of the 

 parasites from one seat of infection to previously healthy connective 

 tissue being all that is required to start a new lesion, or 'secondary 

 growth.' 



In the case of the periosteal sarcoma the tumour may be regarded 

 as being the result of a symbiosis of parasites and one special form 

 of connective tissue. But even in the latter case, when later (or 

 secondary) tumours arise in bones other than that first attacked, there is 

 nothing to indicate that parasites alone have not, by finding a suitable 

 nidus, caused a secondary tumour with all the characters of the first. 



Pigmented Sarcomas. The commoner of these is the melanotic 

 sarcoma, such as arises in the pigmented tissue of the choroid. This 

 type of sarcoma is readily bleached, and may then be examined in 

 the same objective way as any other tissue. When so bleached, I 

 have found in sections of melanotic sarcoma bodies similar to those 

 described above under the head of ' alveolar sarcoma.' I regret that 

 the specimens are missing, so that I am unable to repeat the 

 examination, and to state more exactly the characters of these 

 protozoa-like bodies. 



The resemblance between the primary and secondary lesions 

 in melanotic sarcoma is readily explained in the same way as in 

 the periosteal sarcoma mentioned above. As to the melanotic 

 sarcoma that arises in pigmented moles, I have not made any per- 

 sonal observations, and hence I can offer no opinion as to whether 

 I should regard it as being of protozoan causation or not. 2 It 

 happens that one of the commoner forms of sarcoma, the spindle- 



' Surgical Pathology,' p. 94. 



2 I remember examining an ordinary congenital mole. The pigmented cells of 

 such structures are smaller than those of any melanotic sarcoma that has come 

 to my notice, and I have failed to find in these moles any of the forms described 

 above as protozoa. 



