TUMORS. 469 



Origin. All tumors originate from indifferent or medullary 

 elements, in nearly the same manner as that by which physiolog- 

 ical tissues are produced. No tissue can increase or pass into 

 another, except through the intervening stage of medullary tis- 

 sue, and no tumor arises from a normal tissue without the latter 

 first passing through the same intervening stage. Virchow 

 maintained that the new formation of a tissue the hyperplasia 

 is either homologous (homoeo-plastic, Lobstein) or heterologous 

 (heteroplastic, Lobstein) ; the former meaning a new formation 

 of a tissue, identical or similar to the parent-tissue ; the latter a 

 tissue differing in type from the parent-tissue. This idea cannot 

 be carried out, as every new formation is at first heterologous 

 i. e.j medullary tissue. 



The reason why a tissue sometimes produces a tumor is not 

 understood. This, at least in some instances, appears to be due 

 to a long continued irritation, or to an injury. But in many 

 instances no such cause can be traced 5 neither are we able to 

 explain why the reaction following irritation is, in some individ- 

 uals, an acute or chronic inflammation only, and in others the 

 production of a tumor in addition. 



Tumors are tissues which, so long as they are in connection 

 with the living organism, are living themselves i. e., pervaded 

 by a delicate reticulum of living matter in the same manner as 

 physiological tissues. The type of a tumor is usually that of a 

 physiological tissue ; in other words, there is no tissue constitut- 

 ing a tumor which differs materially from the normal tissues. A 

 difference, however, in many instances, is established, for the 

 reason that the tissue of a tumor remains in an embryonal or 

 medullary condition, without passing on to a more fully devel- 

 oped type, f. i., in myeloma, or else the combination of the tis- 

 sues is different from that which we know to be a physiological 

 type f. i., in cancer. 



It is an easy matter to explain the cause of the formation of a tumor by 

 the terms "general diathesis," or "general or local disposition." Is there any- 

 thing satisfactory in such an assumption ? Is it not more correct to honestly 

 admit that we do not know the real etiology of a tumor ? 



An apparent progress was made by Thiersch (1865) and by Waldeyer 

 (1868), who claimed that the epithelia of cancer arise invariably from genu- 

 ine preexisting epithelia, and that, therefore, cancer can originate only in tis- 

 sues which are offspring of the upper and under germinal layer, and in a 

 physiological condition are constructed of epithelia. These assertions in turn 

 have been disproved by both clinical and microscopical observation. A 

 tumor once formed may gradually involve its neighborhood and grow at the 



