TUMORS. 2(>0 



onic cells that are similar to embryonic connective-tissue cells. 

 Papillomata are composed of cells that are verj^ similar, if not 

 identical, to adult epithelial cells, and are supported by an adult 

 connective-tissue framework. 



Tumor cells are very similar to the cells of normal animal 

 tissues. They have practically the same structure and require 

 the same kind of nutriment. However, they do differ from the 

 normal tissue cells in their power of growth and reproduction. 



Tumor cells are usualh- more susceptil)le to changed environ- 

 ments than normal tissue cells. The nuclei of the cells of a rap- 

 idly growing tumor are usually larger probably because of in- 

 creased functional activit}-. 



The intercellular substance of tumors is as variable as the 

 intercellular sulistance of normal tissues. Tumors having a 

 mesodermal origin usually have an intercellular substance closely 

 resembling that of normal connective tissue and hence maj^ be 

 mucus, fibrous, cartilaginous, or osseous. Tumors C)f an ectoder- 

 mal or an entodermal origin ma}^ appro]iriate the pre-existing 

 tissue framework for their strcima. Some tumors, like some 

 normal tissues, are jaracticalh- devoid of intercellular sul)stance. 

 Again, in some tumors the blood-\-essels are the only intercellular 

 substance, .\natomicalh- the intercellular substance or stroma 

 is an integral part of a tumor and its function corresponds to 

 the function of intercellidar sul)stance of normal tissue. The 

 cells and intercellular substance of tumors ma\' be so arranged 

 that the resulting structure approximates that of normal tissue 

 (histoid tumors), but is never identical to a normal tissue. The 

 dili'erent parts of a tumor may be assembled so that the resulting 

 organization appears as an atypical gland or organ (organoid 

 tumor), or tumors may be composed of structures derived 

 from all three germ layers grouped indiscriminately but liaving 

 some resemblance to an embryo (teratoid tumors.) 



Like normal tissue, tumors are usually nourished, by blood 

 and lymph. The blood and lymph vessels may be structurally 

 the same as normal vessels, or they may be composed entirely of 

 tumor cells. The vessels have their origin from pre-existing ves- 

 sels in the tissue from which the tumors are developed. They 

 may be telangiectatic, cavernous, or plexiform, and then- 

 course is usually along the tumor stroma. Blood and lymph may 

 also permeate the tumor through intercellular spaces, frequently 

 resulting in hemorrhage or lymphorrhage. Some tumors have 

 no blood or lymph supply, their nourishment probably being 

 derived from consumption of normal tissue. 



Nerve cells and axones have been demonstrated in some 



