CHAPTER III 54 



METAPLASIA 



After disposing in the preceding chapter of those cells or 

 tissues which remain in some way below the no rmal in development 

 we will discuss in the following sectionsrthosrwhich in some ' 

 way exceed the normal. In the simplest case, an abnormal ad- 

 vance in development may result from changes in the cell-char- 

 acter, without involving any increase in volume or anv process 

 of division. 



The changes in cell character, exclusive of the last named 

 processes may differ very widely among themselves. Either a 

 breaking down of the cell content, or of a definite part of it, 

 is involved; the organs of the cell, partially or as a whole, be- 

 come incapable of functioning and die, or disappear completelv. 

 Changes of this kind are called regressive , or the transforma- 

 tions show that the cells perform new functions, or thg cytoplasm 

 has been increased in them, or new organs are formed, and the 

 like. Changes of this kind are called progressive . Since inre- 

 gressive changes, the symptoms of degeneration and necrosis are 

 involved which should be kept out of our consideration, only pro- 

 gressive changes are to be treated of in the present chapter. .We 

 will define Metaplasi a as every progressive change of any, cell ' 

 which is not connected with cell-growth and cell-division . 



Since our distinction between regressive and progressive 

 changes is based upon physiological peculiarities of the cells 

 concerned and since, further, in judging of the latter we are of- 

 ten led to conclusions, the drawing of v/hich is made possible by 

 the anatomical character of the cells and tissues, it is evident 

 (56) that we will not always be able to decide with certainty whether 

 a change in the cell body is to be termed progressive or regres- 

 sive. Besides the undoubtedly progressive changes, our discussion 

 should also take into consideration those others for which our 

 present slight knowledge of their cell-li'fo makes no final de- 

 cision possible. 



Metaplasia plays a much more modest role in the abnormal 

 histology of plants than in the animal or human body. In the 

 latter metaplasia from varying causes becomes the foundation of 

 many important, pathological processes, in as much as definite 

 tissues change their character and are transformed into other 

 kinds, To be sure such a transition is possible only between 

 nearly related forms, especially among the different connective 

 tissues. Nevertheless J in metaplasia the original character of 

 the transformed cells can become entirely unrecognizable, for ex- 

 ample, if reticulated connective tissue be changed into fatty 

 tissue. In plants, the number of observed transformations is very 

 much less than in animal tissue and, moreover, in all cases the 

 original character of the plant cells changed raetaplastically 

 remains readily recognizable. The reasons for this are not hard 

 to find. W^ile in the metaplasia of animal tissues the form of 

 the cells is capable of very extensive changes, in plant cells 

 the ffrm remains constantlj?- fixed by the firm cellulose ocverihg 

 af the individual elements. Change in form is made possible only 

 ■ by growth, and therefore is not involved in changes of a purely 

 raetaplaetia character. 



Metaplastic changes are produced in the cells of plants es- 

 pecially by the formation of new cell contents . or by changes oi 

 the membrane .- through growth in thickness. 



■^ SO far as I know, Virchow introduced the term metaplasia . . 

 He states that " persistency of the cells in the changing of the 

 tissue-cha racter , is characteristic of this process^; Vir chow's 

 lecture "Ueber Metaplasie" (in s. Arch. f. path. Anat. 1884, Bd. 

 ynVTI -D. 4-10 ) is also of great interest for non-medical men. 



