The non-malignant growths may present various characters, intermediate between those of the tissues they replace, and those of malig nant structures. In regard to their pathological cause, " we cannot at present go beyond the supposition, that they arise from altered vital properties in some of the molecules of the textures in which they are developed ; so that, instead of being assimilated to these textures, and conforming to the laws of their growth and decay, these molecules grow of themselves in modes more or less peculiar, and more or less independently of the influences of the adjoining living parts. Where these modes are less peculiar, and more dependent upon the nutrition of the adiacent structures, the growths Now although tubercular matter may be I I slowly and insidiously deposited, by a kind of degradation of the ordinary nutritive process, , yet it cannot be doubted that inflammation has a great tendency to favour it; so that a larger quantity may be produced in the lungs, after a pneumonia has existed for a day or two, than it would have required years to generate in the previous mode. But the character of the de posit still rernains the same ; and its relation to the plastic element of the blood is shown by the interesting fact, of no unfrequent occurrence,— ' that, in a pneumonia affecting a tuberculous subject, plastic lymph is thrown out in one part, 'whilst tubercular matter is deposited in another. .Now inflammation, producing a rapid deposi tion of tubercular matter, is peculiarly liable to Spise in organs which have been previously are less abnormal, vary less from these struc tures, and more resemble either hypertrophy or euplastic deposits ; and they do mischief rather from their size and situation than from their intrinsic nature. Where the mode of growth is more peculiar, and more independent of that of the textures in which they arise, the resulting tumours are more abnormal in their nature and mode of developement ; they approach in character to malignant diseases, acting inju riously, not only by their bulk and position, but also by abstracting the nourishment of the body, and tending to supersede the natural structures."' Among the malignant growths, too, there are various shades or degrees of malignancy ; one or more of the characters just now assigned to them being either absent or imperfectly de veloped. Thus there are certain growths which have a tendency to spread through the system, and even to propagate themselves from one individual to another and which agree with true malignant growths in being composed, like them, of cells having a tendency to rapid multiplication, but which yet exert no serious influence upon the general constitutional state, and which cannot, therefore, be properly termed malignant: such are molluscum and porrigo firma. And in other instances we meet with large tumours, producing a very injurious effect upon the surrounding textures, and exerting a very serious influence upon the system at large; the malignancy of which, however, is doubtful, because they show no tendency to reappear in other parts of the body. The origin of all these growths is involved in great obscurity ; but there does not appear to the writer to be any thing so specific in their character as to require the supposition that their germs are introduced into the body from without. It is true that when they have once established themselves they may be propagated by inoculation, which transplant.; some of the cells or cell-germs into a new locality; and the appearance of the dis ease in parts of the same body distant from those which were first affected, is probably due to the diffusion of the germs by the current of the circulation. But this power of reproduc tion is by no means limited to malignant growths, since it belongs to all cells at a cer tain stage of their developement. And, as Dr. W. Budd t has remarked, the causes which have been supposed to induce cancer are not such as can, in any intelligible way, favour the Introduction of germs from without the body. Thus in chimney-sweeps and others the conti nued application of soot has been observed to be followed by the occurrence of cancer in the scrotum in such a number of cases, as to justify the inference that it has been the exciting cause; and the often-repeated contact of a tobacco-pipe with the lip has also been considered a cause of cancer of that part. But neither of these causes can in any conceivable way promote the developement of cancer from extrinsic germs. We are quite in the'dark, however, as to the mode in which any perversion of the ordinary nutritive processes arising from external irrita tion of whatever kind, can give rise to struc tures so peculiar in their nature arid history as are the various forms of cancerous growths. For a detailed account of their characters as unveiled by recent microscopic researches, the reader must seek elsewhere ; since all that me can here attempt is to give a general idea of their peculiar nature. (See PRODUCTS, MORBID.) The greater part of every true malignant growth is made up of cells, which, instead of under going transformation into other kinds of tissue, continue in their original state, and enjoy the power of rapid multiplication. In the harder forms of cancer the masses of cells are traversed by bands of solid fibrous texture, and such are of slow growth, and may remain with but little change for many years, apparently because the pressure to which they are subjected prevents their rapid increase. But the softer forms are 'composed almost entirely of cells, and these of the most rapidly multiplying character ; so that, in the rapidity with which they shoot up, they remind us of the vegetable fungi. Now the influence of either of these forms of morbid growth upon the constitution is very decided, and distinguishes them from non-malignant structures ; but this is rnore evident, the more time is afforded for the manifestation of their effects. It is evident even from the appearance
of the subject of them that the blood must be in a very depraved state, for there is a peculiar 0 dirty sallowness about the complexion which is seen in no other disease ; the emaciation reaches a point unequalled under any other circumstances ; and accidental injuries which may occur during the progress of the malady are but very imperfectly repaired. In their de leterious effects upon the character of the circu lating fluid, therefore, we may not improperly compare cancer-cells with pus-globules.
General summary.—Frorn what has been stated it appears evident, that the process of nutrition essentially consists in the growth of, the individual cells composing the fabric; and that these derive their support from the organic, compounds with which they are supplied by the blood, just as the cells composing the sim plest plants derive theirs from the inorganic; elements which surround them. And as diffe-1 rent species of the latter select and combine; these in such modes and proportions as to gise, rise to organisms of very diversified forms and, properties, so is it easily intelligible that the, different parts of the fabric of the highest ani mals, whether normal or abnormal, should, exercise a similar selective power, in regard to the materials with which the blood supplie4 them. The structure composing every separate portion of the body has what rnay be termed a special or ciecrive affinity for some particular constituents of the blood; causing it to abstrag from that fluid and to convert into its own substance certain of its elements : and this 13 exercised riot only in regard to the normal con stituents of the blood, but also towards morbid matters which may be circulating with it. 0,1 the causes which enable the cells of animal 03 vegetable structure to exercise these varied attractions, our knowledge is at present very limited. It will probably long remain an ulti mate fact in physiolog,y that cells have the power of growing from germs, of undergoing certain transformations, and of producing germs that will develope other cells similar to them selves, just as it is an ultimate fact in physics that masses of matter attract each other ; or in chemistry, that the molecules of different sub stances have a tendency to unite, so as to form a compound different from either of the ele ments. It is of such ultimate facts that the science of vitality essentially consists. The conditions under which the assimilating power operates are, however, like the laws of chemical affinity, freely open to our investigation ; and it is a great step in the progress of the inquiry to become aware that these are so closely con formable throughout the organized world, as we have endeavoured to show them to be.
It may be stated as a general fact, that in assimilating or converting into its own sub stance matter which was previously unable to exhibit any of the manifestations of life, every cell thereby participates in the process of orga nization and vitalization ; for by the new cir cumstances in which the matter is placed its sensible properties are altered,—some which were previously dormant being now caused to manifest themselves, whilst others, which were previously evident, become latent. No mat ter that is not in a state of organization can exhibit these properties, which,froin their being peculiar to living bodies, and altogether diffe rent from those of which physics and chemistry take cognizance, are termed vital ; and it may also be asserted that no matter which exhibits perfect org,anization is destitute of the peculiar vital properties belonging to its kind of struc ture. (See LIFE.) IIence every act of nutri tion is, in fact, the creation of a new amount of vital force ; and when that vital force has been expended, no more can be developed except by the nutritive process.
From the foregoing details it further results that we must regard each part of the organism as having an individual life of its OW11, whilst contributing to uphold the general life of the entire being. This life, or state of vital action, depends upon the due performance of the func tions of all the subordinate parts which are closely connected together. The lowest classes of organized beings, and even the highest at an early stage of their embryonic developement, are made up of repetitions of the same ele ments; and each part, therefore, can perform its functions in great degree independently of the rest. But in ascending- the scale or in tracing the advancing developement of the em bryo, we find that the individual lives of the cells become gradually merged (so to speak) in the general life of the structure ; for they be come more and more different from each other in function, and therefore more and more de pendent on each other for their means of sup port ; so that the activity of all is necessary for the maintenance of any one. Bence the inter ruption of the function of any important organ is followed by the death of the entire structure; because it interferes with the elaboration, circu lation, and continual pur'fication of that nutri tious fluid which supplie he pabulum for the growth and reproduction oft .ndividual cells. But their lives may be prolonged for a greater or less duration after the suspension of the regular series of their combined actions; hence it is that molecular death is not always an im mediate consequence of somatic death. (See DEATH.) But if the function of the part have no immediate relation to the indispensable actions just referred to, it may cease without affecting them ; so that molecular death triay take place to a considerable extent without somatic death necessarily resulting.