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inate ; but their history proves them to be non-hereditary. 

 So far as we can learn by the aid of the microscope, they 

 are not caused by parasites, and they are not of a nervous 

 origin. However, there is some slight indication that they 

 may be of a mechanical or inflammatory origin ; but admit- 

 ting this, it would not give us all the causal factors ; since 

 there must have been some unknown favorable condition of 

 the system to produce the morbid growth that follows the 

 mechanical irritation. These tumors are very frequently 

 found upon regions of the body which, on account of their 

 location, are little liable to irritation. For instance, in 

 several cases which were brought to the college free clinic, 

 these tumors were found upon the ears, the breast, the 

 iijside of the legs and on the sides of the neck — places little 

 liable to irritation ; hence, could not be so produced except 

 by uncommon accidental mechanical irritation. It is true 

 that after the tumors have begun to grow, mechanical irri- 

 tation will augment their development, cause them to grow 

 more rapidly and larger. 



These tumors are composed of multiplying or prolifera- 

 ting cells ; the growth or enlargement is not due simply to 

 an increase in the size of the individual tumor cells, but to 

 a multiplication and enlargement of the cells. 



These tumors are vascular ; are supplied with neutri- 

 ent blood by branches from the vessels of the subcutaneous 

 connective tissue, in which they are generally found im- 

 bedded. 



The shape of these tumors depends upon their location ; 

 as a rule, they approximate a spherical form. If they are 

 crowded or pressed by a limb or by another tumor, they 

 will assume a shape corresponding to the pressure to which 

 they are subjected ; hence, they may be oval, pear shaped, 

 or somewhat flattened, but when they occur ou a free surface 

 they generally approximate a sperical form. 



According to one classification, tumors are divided into 

 three groups : 



1. The Simple or Histoid tumors which are composed 



