1.905.] On the Cytology of Malignant Growths. 



339 



Having completed that foregoing brief survey of the structures and changes 

 that occur in the cells of a healthy rectum, we are in a position to consider 

 the features that arise on the early development of a cancer in this region. 

 In the case of the neoplasm we are especially concerned with, the area 

 involved was very small, barely a centimetre in diameter, and this area 

 marks the original seat of the disease. The central portions were but slightly 

 ulcerated or broken down, whilst the margins were hardly at all raised. The 

 essential details of the structure as shown near the edge of the growth are 

 figured in fig. 1. 



Towards the periphery of the growth the columnar cells are scarcely 

 displaced, but they exhibit a more or less altered appearance when compared 

 with the still healthy cells in their vicinity. There can, in fact, be traced a 

 narrow and not very sharp line of demarcation that distinguishes the 

 cancerous from the non-cancerous epithelial elements. A consideration of 

 the structure of the cells in this region makes it perfectly clear that the 

 growth has not proceeded from a more remote centre to invade the healthy 

 mucosa, but that the cells of this layer are themselves assuming the peculiar 

 characters of the growth. In other words we are confronted with a primary 

 transmutation of normal and functional cells into those of cancerous tissue. 

 The tumour was small and flat, the change visible at its margin having 

 presumably proceeded centrifugally over the more developed central area. 



Thus the growth, regarded as a whole, must be considered as having 

 originated from a relatively large number of functional epithelial cells by a 

 direct conversion of them into neoplastic elements. No other interpretation 

 seems reconcilable with the facts of the case, but we may defer the theoretical 

 conclusion involved therein for subsequent consideration. 



But, notwithstanding the evidence for the marginal spread of the growth 

 by a direct alteration of the cells in this region, when once the change has 

 been effected in them, the cancerous cells begin on their own account to 

 invade the deeper layers of tissue situated beneath the epithelium. This is 

 illustrated by fig. l,g. The general nature of the process of invasion is so 

 well known as to call for no specially detailed description here. It will be 

 noted, however, as shown in the illustration, that the ingrowing cancerous 

 tissue long retains many of the features characteristic of the particular 

 epithelium from which it has sprung. This is, of course, not uncommon, 

 especially in the case of glandular tumours (fig. 1, b). 



The marginal zone of demarcation between the diseased and healthy tissue 

 is distinguished at its periphery by a barely perceptible increase in the size of 

 the elements that compose it. Immediately within this outermost limit a 

 rapid multiplication of the cells is seen to be taking place, and even in the 



