Pathological Si^^nUicancc of Tumors. 331 



manner the tunuir is disseminated widely to the various organs, 

 we speak of the generalisation of the tumor. This lodgment and 

 development of daughter nodules from the cells which have be- 

 come freed from a tumor, an actual form of seeding by trans- 

 plantation, is met also at contact points on mucous and serous 

 surfaces. For example, an ovarian tumor may become dissem- 

 inated all over the peritoneum by having its cells loosened and 

 scattered over the serous membrane ; a tumor of the costal pleura 

 may become transplanted to the visceral pleura ; one of the 

 upper lip to the lower lip. The cellular elements of the growth 

 in such instances are freed and distributed by the movements of 

 the viscera, or by the friction of contiguous surfaces. 



All secondary growths correspond closely with the primary 

 tumor from which they arose in their histological structure; 

 where a cancer of the gum metastasizes to the retropharyngeal 

 lymph glands and lungs the metastatic formations are composed 

 of squamous epithelial cells just as is the primary tumor. They 

 need not necessarily be smaller than the original giowth, and 

 are often of larger size than the latter. 



Tumors which can be completely removed, which are not metastatic 

 and do not recur, are ordinarily called, from the clinical point of view, 

 benign (innocent) ; those which penetrate into the adjacent tissues and are 

 removed in their entirety with difficulty, or are recurrent and give rise 

 to metastases, are called malignant (harmful). To the extent that experi- 

 ence shows that one or othe-- of these results may generally be expected 

 in operations for removal, the classification into these two types may be 

 accepted; but the differences are not to be depended upon, as some tumors 

 which do not form metastases recur if not completely removed, and 

 tumors which are ordinarily regarded as benign may occasionally produce 

 metastases; and, again, well-known malignant growths often remain strictly 

 localized and harmless for a long time, and if they are removed early 

 enough will not recur. 



As a further factor by which tumors may affect the system, 

 it should be recalled that within these neoplasms all sorts of 

 metabolic products and decomposition substances are being freed, 

 and these may by absorption have toxic influences upon the 

 possessor of the growth. It is quite common to meet with in- 

 flammatory changes in the tissue about a tumor and the growth 

 itself may be found richly infiltrated with immigrating leucocytes, 

 or rnay be found undergoing suppurative or gangrenous changes. 

 This may be due to the fact that tumors which happen to be situated 

 on exposed surfaces are invaded by bacteria, and the toxines 

 of the latter excite inflammation ; but there is little doubt that 



