CANCEROUS TUMORS. 3 



cancer in almost every instance in which a non-malignant 

 growth is removed by their caustic pastes or plasters. 



I fully sympathize with the wish thus expressed, but I warn 

 you at the beginning that you have not much to expect from 

 me in this direction. The best knowledge of those who know 

 most of this matter is not j-et ripe enough to deal satisfactorily 

 with the question of prognosis in very many cases, and I take 

 it that the question of prognosis is involved in the sort of di- 

 agnosis that the general practitioner wants to make. To this 

 subject I will briefly recur in the sequel. Meanwhile I beg j^ou 

 to put all questions of practical application out of your minds, 

 and join me in considering the subject from the point of view 

 of medical science, rather than from that of medical or surgi- 

 cal art. 



I begin then by drawing your attention to some of the more 

 striking features in the general advance of our knowledge of 

 the structure of cancer, and especially since the year 1865, when 

 the publication of the work of Thiersch marks an epoch. The 

 previous history of the subject I will pass over as briefly as 

 possible. Suffice it to remind you that in the earlier days of 

 histological investigation the followers of Schwann supposed 

 cancerous and other tumors to arise by free cell development 

 in a formless blastema exuded from the blood-vessels. The 

 causes of the specific characteristics of individual growths 

 were then naturally sought in the blastemata, and the pecu- 

 liarities attributed to the blastemata were accounted for by 

 supposing them to depend on special morbid conditions or 

 dyscrasiae of the blood. 



The great name of Rokitanski, at whose hands it found its 

 ripest development and most masterly expression, induced the 

 general acceptance of this hypothesis, and it was long the pre- 

 vailing doctrine in the schools of Europe and America, in spite 

 of the circumstance that the most eager and searching inves- 

 tigations of the physiological chemists utterly failed to discern 



