MALIGNANT TUMOURS. 411 



characters of readiness to -ulcerate may be imitated by innocent 

 tumours after injuries, or in exposure to continued irritation ; for 

 they resist these things with less force than the similar natural 

 parts do. Hence sloughing and ulcerating fibrous, erectile, and 

 other tumours, have been often thought cancerous, and so de- 

 scribed. The respective tendencies to ulcerate can therefore be 

 counted only as constituting differences of degree between the 

 innocent and malignant tumours. We may speak of a liability 

 in one case, of a proneness in the other. 



" 4ith. The softening that often precedes the ulceration of 

 malignant growths can hardly be considered separately from the 

 minute account of their structure. I therefore pass by it, and 

 proceed to the fourth distinctive character, which is to be noticed 

 in the modes of their ulceration. 



" This is, that the ulcer which forms in or succeeds a malig- 

 nant growth has no apparent disposition to heal ; but a morbid 

 substance, like that of which the original growth was composed, 

 forms the walls or boundaries of the ulcer ; and as this substance 

 passes through the same process of ulceration which the primary 

 growth passed through, so the malignant ulcer spreads and makes 

 its way through tissues of all kinds. 



" In contrast with this character of malignant growths, it is 

 observable that beneath and around an ordinary ulcer of the 

 natural tissues, or of an innocent tumour, we find the proper 

 tissues unchanged; or perhaps infiltrated and succulent with 

 recent lymph, or the materials for repair; or somewhat indu- 

 rated with lymph already organized. The base and margins 

 of a cancerous ulcer are themselves also cancerous ; those of a 

 common ulcer are infiltrated with only reparative or inflamma- 

 tory material. In like manner, if ulceration extend through 

 an innocent growth, it may destroy it all, and no similar growth, 

 will form in the adjacent parts, replacing that which has been 

 destroyed ; but in the ulceration of cancer, while the cancerous 

 matter is being constantly discharged by sloughing or ulcera- 

 tion from the surface, new matter of the same kind, and in more 

 abundance, is being formed at some distance from the surface ; 

 so that in a section through an ulcerated cancer, one does not 

 arrive at healthy tissues till after passing through a stratum of 

 cancer. 



" 5^A. Malignant tumours are again characterised by this, 



