294 TUMORS. 



form depend, of course, upon the situation of the primary tumor and the 

 distribution of the vascular channels through which dissemination occurs. 



Metastasis affords one of the most 

 noteworthy examples of the great prolif- 

 erative capacity of the cells of malig- 

 nant tumors. For in the metastasis of 

 normal tissue cells, such as not infre- 

 quently occurs after injuries to the bones 

 or the liver, for example the so-called 

 parenchyma cell emboli the transported 

 cells invariably soon die and are disposed 

 of as foreign bodies. But the exalted 

 proliferative capacity of detached tumor 

 no. I.-A tumor-ceii emboiu* growing cells enables them in spite of adverse 

 conditions to establish and maintain fresh 



foci of vigorous tissue growth. 



The Malignancy of Tumors. Not less variable than the size, mode of 

 growth, and structure of tumors is their significance in the organism. 

 It is customary to classify tumors, for practical purposes, as malignant 

 and benign, and for a long time malignant tumor and cancer or carcinoma 

 were synonymous terms. Now w r e know that other tumors as well as car- 

 cmomata are malignant, and, furthermore, contrary to the former belief, 

 that malignancy does not depend upon any specific extracellular agent in 

 the tumor. By the malignancy of a tumor is not meant merely the grav- 

 ity of its presence, for a simple fat tumor, by pressing on the trachea, 

 may lead to suffocation, and any tumor may secondarily cause death by 

 haemorrhage. The real elements of malignancy in a tumor are: 1. 

 Invasion of adjacent tissues by eccentric or peripheral growth. 2. The 

 tendency to local recurrence after removal. 3. The formation of metas- 

 tases. 4. An interference with the nutrition and general well being 

 of the body, which may give rise to a condition known as cachexia. 

 The modes of invasion of surrounding tissues and the formation of me- 

 tastases have been considered above. The tendency to local recurrence 

 after removal is probably, in most cases, due to the incomplete removal 

 of the peripheral infiltrating cells. These may be very few in number 

 and lacking in characteristic structural features, but are none the less 

 endowed with the capacity of proliferation and development into a new 

 and similar tumor at or near the seat of the one extirpated. The infil- 

 trating peripheral cells may remain dormant for a long time after an 

 operation, or may immediately commence to grow. But the mere fact 

 that a second tumor develops in the place of one removed does not imply 

 malignancy, since this may result from a continuance of the conditions 

 which induced the first. 



The drain upon the system by the rapid growth of a tumor, together 

 with the absorption from it into the body of deleterious putrefactive ma- 

 terials, from sloughing, ulceration, and degeneration, or the occurrence 

 in it of local infection with various micro-organisms may give rise to 

 fever and other constitutional disturbances. Or, the tumor may induce 



