TUMORS. 361 



rounding tissues (infiltration) and reducing the probability that some 

 of the cells will be carried to distant parts by the currents of the 

 fluids circulating in the tissues (metastasis). It follows that the 

 presence of intercellular substances having these effects must re- 

 duce the degree of malignancy of the whole growth if they are 

 present throughout its substance. This argument is borne out by 

 the results of experience. The sarcomata might be arranged in a 

 series according to their degrees of malignancy, beginning with 

 those that are most malignant, and have little intercellular substance, 

 and cells which are only slightly, if at all, differentiated, and end- 

 ing with those that can hardly be considered malignant, and which 

 have such an abundant fibrous intercellular substance that their 

 structure closely agrees with that of fibroma. In fact, no sharp 

 line between these sarcomata and the fibromata can be drawn. The 

 two classes of tumor merge into one another : they have the same 

 origin, and differ only in the behavior of their cells in the exercise 

 of their formative activities. Those differences are, however, of the 

 utmost clinical importance. 



The sarcomata are classified, according to the characters of 

 their component cells, into the round-cell, spindle-cell, giant- 

 cell, melanotic, etc., varieties. They are also subdivided ac- 

 cording to the way in which those cells are arranged. The 

 alveolar sarcomata, for example, consist of groups of cells en- 

 closed in the meshes of a fibrous network. These names are, 

 however, more descriptive than indicative of essentially distinct 

 kinds of tumor, and the demarcation between the different varie- 

 eties is not a sharp one. Many sarcomata consist of cells of 

 various shapes, either in different parts or intermingled throughout 

 the growth. This necessitates the insertion of mixed varieties be- 

 tween the above groups of distinct and relatively pure types. Fur- 

 thermore, the cells not only differ in shape, but also in size, so that 

 a distinction may be made between the small round-cell sarcom- 

 ata and the large round-cell variety ; but notwithstanding the 

 fact that this grouping is somewhat artificial, it has a certain clinical 

 value, because it indicates in a rough way the degree of differ- 

 entiation attained by the tumor, and for this reason it will be well 

 to adhere to this classification and to consider the purer types sepa- 

 rately, bearing in mind that the mixed forms of sarcoma possess 

 characters intermediate between those of the simpler forms upon 

 which the classification is primarily based. 



