Causes of Tumors. 335 



the occurrence of dermal proliferatimis ( pai)ill(iinata ) in a number 

 of horses in the same stable. 



However, a great number of objections have been raised against 

 the parasitic hypothesis, especially by Ribbert, which leave this 

 method of causation in extreme doubt. In the first place the 

 various forms of tumors always have their fixed tissue-charac- 

 teristics, and the cells of the metastatic nodules , invariably con- 

 form with th(^se of the original growth ; if an infection were the 

 cause of the tumors it would always have to cause the production 

 of the same kind of cells in the various organs (that is, the cause 

 of a cylindrical cell cancer in the intestine would have to be 

 able to form cylindrical intestinal epithelium in the interior of 

 the liver; the cause of a squamous epithelioma would have to 

 form keratous flat epithelial cells in the lymph glands). How 

 that could occur cannot be understood; it would have to be 

 assumed that the cells were so intimately associated with the 

 parasites that both should always go together and grow together. 

 If such symbiosis be claimed to actually exist, then,, as Ribbert 

 logically argues, it must be assumed that the microorganism 

 invariably divides at the same time as the tumor cells so that 

 one of its offspring may be present in each of the two new 

 cells. "If this be not essential, it may be asked how the cells 

 which do not contain parasites come to proliferate any further. 

 If they are able to multiply, however, without the existence 

 of their parasites, why was it of essential importance that 

 the latter should have ever been present?" (Ribbert). Then 

 there is the established fact that every tumor grows from its own 

 substance under direct pressure contact from the contiguous 

 parts, and the surrounding tissue does not become infected; there- 

 fore the parasite would have to confine its multiplication strictly 

 within the tumor cells. This would be strange ; and the question 

 naturally arises, why, for example, the neighboring- epithelia 

 which are quite like those of a skin cancer do not furnish equally 

 favorable soil for the development of the microorganisms. In 

 the end, as Ribbert emphasizes, we should have to assume 

 that for every new growth, for every type of cell of malignant 

 tumors, there exists a special type of infectious agent incapable 

 of infecting otlier cells, as one special form for cylindrical cell 

 cancers, another, for squamous cell cancers, etc. The genesis of 

 tumors would become progressively more and more complicated 

 if such ideas w^ere to prevail. 



