444 OF NUTRITION. 



frequently encysted) are sometimes met with as outlying portions of the 

 gland itself. There is another class of objects, to which Tumors come into 

 close relation, and which must be referred, like them, to a local excess of 

 formative activity; these are the "supernumerary parts" which are not un- 

 frequently developed during foetal life, as for example, additional fingers and 

 toes. It seems absurd to refer these, formed as they are by simple outgrowth 

 from the limbs to which they are attached, to the "fusion of germs" which 

 has been hypothetically invoked to explain more important excesses, as 

 those of additional limbs, double bodies, or double heads ; and yet from the 

 lower to the higher form of excess, the transition is so gradual, that what is 

 true of the former can scarcely but be true of the latter. Hence even com- 

 plete "double monsters" must be regarded, not as having proceeded from 

 two separate germs which have become partially united in the course of their 

 development, but from a single germ, which, being possessed of an unusual 

 formative capacity, has evolved itself into a structure containing more than 

 the usual number of parts, and comparable to that which may be artificially 

 produced by partial fission of the bodies of many of the lower animals. 1 



358. We can scarcely fail to recognize, throughout this whole series of 

 abnormal productions, the operation of a similar power. In the formation 

 of a supernumerary part, this has been sufficient not merely to produce the 

 tissues, and to develop them according to a regular morphological type, but 

 to impart to the fabric thus generated a separate and even an independent 

 existence; thus involving an additional finger or thumb on each hand, a 

 double pair of arms or legs, a double head or trunk, or even a complete 

 double body. In the hypertrophy of a regular or normal part, the new 

 tissues are still developed according to a regular morphological type ; but 

 they have not the power of individualizing themselves (so to speak), aud 

 are so incorporated with the normal elements as to augment the size of the 

 existing organ. In the formation of a tumor, on the other hand, whilst its 

 component tissues are themselves perfectly formed, aud have a marked power 

 of independent growth, the mass composed of them is altogether amorphous, 

 its configuration being usually determined rather by the physical conditions 

 under which it is produced, than by any peculiar tendencies of its own ; so 

 that we recognize the action of the formative power, undirected by that 

 morphological nisus, which normally models (so to speak) the growing tis- 

 sues into the likeness of the organ to which they belong. But further, in 

 many of the large class of tumors distinguished as "malignant," the develop- 

 ment of tissue has not gone to the extent of producing any of those species 

 of which the body is normally constituted ; and in this respect, as well as in 

 their tendency to rapid degeneration, the vital endowments of their elements 

 must be reckoned as below those of the normal tissues. It is not always easy 

 to draw the line between certain tumors and supernumerary parts, especially 

 when the production of the former is symmetrical ; but the first appearance 

 of the latter never takes place save during embryonic life, and their struc- 

 ture is more complex, and is more conformed to the plan and construction 

 of the body at large, than is that of tumors, whose production may take 

 place at any period of life. And between those tumors which are known as 

 "piliferous" and "dentigerous cysts," and those encysted embryos (usually 

 incomplete in their formation) which are sometimes found in the bodies even 

 of males, it is impossible to establish any line of demarcation sufficiently 

 precise, to prevent our recognizing them as all having the same origin, and 



1 Sec Prine. of Oomp. Phys., \ 475, Prof. Vrolik in Cyclop, of Anat. and Phys., 

 art. Teratology, vol. iv, p. 976; and Prof. Allen Thomson on Double Monstrosity, 

 in Edinb. Monthly Journal, June and July, 1844. 



