608 OF NUTRITION. 



may of themselves become sources of irritation ; and the perversion of the 

 structure and functions of the part renders it peculiarly susceptible of the 

 influence of external morbific causes. These views, at which several recent 

 Physiologists and Pathologists have arrived on independent grounds, seem to 

 reconcile or supersede all the discordant opinions which have been upheld at 

 different times regarding the nature of Tubercle ; and lead to the soundest 

 views with respect to the treatment of the Diathesis. 



809. We frequently meet with abnormal growths of a Fatty, Cartilaginous, 

 Fibrous, or even Bony structure ; which result from the development of these 

 tissues in unusual situations, and appear to originate in some perverted action 

 of the parts themselves. But there is another remarkable form of disordered 

 Nutrition, which is concerned in producing what have been termed hetero- 

 logous growths, that is, masses of tissue, differing in character from any 

 which is normally present in the body. Most of these are included under 

 the general designation of Cancerous or Fungous structures ; and it has been 

 shown by Miiller and others, that the new growth consists of a mass of cells; 

 which, like the Vegetable Fungi, develope themselves with great rapidity ; and 

 which destroy the surrounding tissues by their pressure, as well as by ab- 

 stracting from the Blood the nourishment which was destined for them. 

 These parasitic masses have a completely independent power of growth and 

 reproduction ; and it seems difficult to refuse them the character of distinct 

 existences. They can be propagated by inoculation, which conveys into the 

 tissues of the animal operated on, the germs of the peculiar cells that consti- 

 tute the morbid growth ; and these soon develope themselves into a new 

 mass. It seems to be by the diffusion of the germs produced in one part, 

 through the whole fabric, by the circulating current, that the tendency to re- 

 appearance (which is one great feature in the malignant character of these 

 diseases) is occasioned. Yet there is no evidence, that the first production 

 of a Cancerous growth is due to germs introduced from without ; in fact, as 

 it appears to the Author, the history of its origin, as well as the analogy of 

 similar cases, makes it far more probable, that the Cancer-cell is but an abnor- 

 mal form of the ordinary tissue-cells of the body, being, in fact, a cell which 

 possesses to an unusual degree the power of reproduction, instead of under- 

 going those transformations by which it would be converted into other 

 kinds of tissue. 



a. Several instances have been recently published, of the occurrence of Vegetable organ- 

 isms as parasites upon the Animal body. That in some of these a true Plant, possessing a 

 regular apparatus of nutrition and reproduction, has arisen from a germ introduced from 

 without, there can be little question ; but in other instances (as in the case of the crusts of 

 Porrigo favosd), it has been assumed that the organization is Vegetable, merely because it 

 consists of a mass of cells capable of extending themselves by the ordinary process of mul- 

 tiplication. But it must be remembered, that the cellular organization is common to Ani- 

 mals as well as to Plants ; being the only form that manifests itself at an early period of 

 development in either kingdom, and remaining throughout life in those parts which have 

 not undergone a metamorphosis for special purposes. Hence to speak of Porrigo favosa, or 

 any similar disease, as produced by the growth of a Plant within the Animal body, appears 

 to the Author a very arbitrary assumption ; the simple fact being, in regard to this and many 

 other structures of a low type, that they present the simplest or most general kind of organ- 

 ization. Their nature must be decided by their Chemical constitution ; and this, in the case 

 of the Porrigo favosa, appears to be unquestionably Animal. 



b. There seems a strong probability in the idea, that the propagation of many diseases by 

 inoculation, essentially consists in the transplanting of cell-germs from the body of one ani- 

 mal to that of another. Thus the Vaccine Vesicle appears to be made up of an aggregation 

 of distinct cells, to which we may very fairly attribute anorigin of this kind. But this seems 

 rather true of diseases which manifest themselves by a local development of cellular struc- 

 tures, such as Cancer and Cow-pox, than of such as Hydrophobia, Plague, Poisoning by 

 Serpents, &c., in which the symptoms are referrible, more or less clearly, to an alteration in 

 the character of the Blood, by the introduction of a substance acting as a ferment ( 70S). 



