MALIGNANT TUMOURS. 409 



distinctive characters are to be sought in their arrangement, 

 rather than in the form of the cells themselves. Extended obser- 

 vations have shown that cells undistinguishable from those of 

 cancer may be found in certain sarcomata, in glandular growths, 

 and even in healthy parts, as in the pelvis of the kidney, and the 

 prostate vesicle. Paget says — 



" 1st. The intimate structure of malignant tumours is usually 

 not like that of any of the fully developed natural parts of the 

 body, nor like that which is formed in a natural process of 

 development, repair, or degeneration. Many of the cells of 

 cancers, for example, may be somewhat like gland cells, or like 

 epithelium cells, yet a practised eye can distinguish them even 

 singly. And much more plainly their grouping distinguishes 

 them ; they are heaped together disorderly, and seldom have any 

 lobular or laminar arrangement, such as exists in the natural 

 glands and epithelia, or in the innocent glandular or epithelial 

 or epidermal tumours. These innocent tumours are really imi- 

 tations, so far as their structure is concerned, of the natural 

 parts; and the existence of such imitations in any tumours 

 makes the diversity — the heterology, as it is called — of the 

 malignant tumours appears more evident. Still this rule of 

 dissimilarity of structure in malignant tumours is only general. 

 The other properties of malignancy may be sometimes observed 

 in tumours that have apparently the same structure as those 

 that are generally innocent. . . . 



" 2d. Malignant growths may have the character of infiltra- 

 tions, i.e., their elementary structures may be inserted, infil- 

 trated, or diffused in the interspaces and cavities of the tissues 

 in which they lie. Thus, in its early stage, a malignant tumour 

 may comprise, with its own proper elements, those of the organ 

 in which it is formed ; and it is only in its later life that the 

 elements of the tissue or organ disappear from it, gradually de- 

 generating and being absorbed, or possibly yielding themselves 

 as materials for its growth. 



" Thus a hard cancer of the mammary gland includes in its 

 mass a part, or even the whole, of the gland itself, as if there 

 were only a conversion of the gland tissue ; and one may find 

 within the very substance of the cancer the remains of the lacti- 

 ferous tubes involved in it, and with the microscope may trace in 

 it the connective tissue that separated the gland -lobes^ and the 



