300 TUMORS. 



incited by the tubercle bacillus, the lepra bacillus, etc., which have 

 sometimes been classed with tumors and called infectious granulomata. 

 The reader is referred to the sections dealing with the nature of the 

 inflammatory process in general, page 123, and to the introductory section 

 in the present chapter for a review of the differences in the conception 

 of the inflammatory processes and tumor formation. 



Attention has recently been called, in connection with tumors, to cer- 

 tain forms of yeasts or blastomycetes as excitants of new tissue growths, 

 but these also appear to be inflammatory. The cultivation of yeasts from 

 the tissues of malignant or other tumors is of no more significance than 

 the cultivation of bacteria under similar conditions. 



The nearly uniform failure in the attempts to transplant tumors from 

 one species of animal to another, and the absolute failure to cultivate, 





FIG. 143. EPITHELIAL-CELL "INCLUSIONS" IN TUMORS. 

 Showing various forms. From carcinoma. 



either directly or by inoculation, any constant organisms from them 

 which are capable of inducing experimental tumor growths, speak with 

 much force against the notion of the parasitic origin of malignant tumors. 

 Moreover, the great diversity in character and in the inconstancy of oc- 

 currence of the objects which have been regarded as of possible signifi- 

 cance in tumors, greatly diminishes the plausibility of the claims which 

 have been made for them. 



It is much to be regretted that most of those who advocate the para- 

 sitic nature of tumor excitants should be so engrossed with the alleged 

 parasites that they largely ignore the dominant characters and the life 

 history of the tumors themselves, especially of malignant forms, and the 

 fundamental distinctions between these and such inflammatory growths 

 as may superficially resemble tumors and which are undoubtedly often 

 incited by various kinds of micro-organisms. 



We do not of course assert that tumors cannot be incited by parasites, 



