THE STRUCTURE OF A ROUND-CELLED SARCOMA 113 



mitosis, as at 4, it has the ordinary characters of a dividing tissue- 

 cell. 



On comparing Fig. 42 with Fig. 32 (p. 91), it will be seen that 

 there is no essential difference between this round-celled sarcoma 

 and the alveolar sarcoma ; both are based on changes in preexisting 

 connective-tissue cells. In neither do these cells take any material 

 part in forming the tumour by proliferation ; only with great diffi- 

 culty is a dividing connective-tissue cell to be found, and then it is 

 seen to have the ordinary characters of such a cell. The difference 

 in the two growths consists in the behaviour of the parasites. In 

 the round-celled sarcoma the parasites collect together and form 

 large masses of small bodies, many of which have the appearance of 

 involution-forms, whilst in the alveolar sarcoma the parasites are 

 evenly distributed throughout the tumour, and the products of 

 their subdivision show signs of intense vitality and infecting power. 



What accounts for the difference between this tumour and the 

 alveolar sarcoma ? 



The extent to which molar necrosis is observed in affections of 

 the testis is well known to be in excess of that seen in similar 

 diseases, whether cancer, sarcoma, syphilis, or tuberculosis, of other 

 organs. This fact is easily accounted for by the character of the 

 blood-supply of the organ, which is supplied by long, slender, and 

 tortuous branches of a single artery, itself of great length and 

 subject to temporary, partial, or complete occlusions. The differ- 

 ences observed in the bodies I have described above as protozoa, in 

 the alveolar sarcoma of the breast and the sarcoma of the testis 

 respectively, are evidently due to a slight difference in the vitality 

 of the parasites in the two cases. In the former the parasites were 

 in full vigour and showed no signs of degeneration, but invaded the 

 tissue, destroying it and reducing it to a liquid detritus, as shown by 

 the cavity in Fig. 30 ; whilst in the sarcoma of the testis the process 

 was a slower one, and the bulk of the parasites congregated in 

 masses (Fig. 40 ; 2), and their subdivision resulted not so much in the 

 formation of well-defined gem mules and stellate bodies as of granular 

 and reticular involution-forms. I remember that it was on malignant 



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