May 28, 1897.] 



SCIENCE. 



829 



There are, however, great difficulties in ex- 

 plaining all chronic interstitial inflamma- 

 tions by this doctrine, and I must take side 

 with those who admit the occurrence, for 

 example in the kidney and in the liver, of 

 primary interstitial inflammations char- 

 acterized by proliferation of the connective 

 tissue and endothelial cells. 



Indeed, it seems to me that "Weigert's 

 formula is too narrow to cover all of the 

 observed facts concerning cell-proliferation. 

 Essential features of the theory that cells 

 cannot be directly stimulated to growth by 

 external agents were present in Boll's doc- 

 trine of border warfare between neighbor- 

 ing cells. Weigert's presentation of this 

 theory is in a far more acceptable shape 

 than that of Boll. A still more compre- 

 hensive statement of the general theory is 

 that cells are incited to growth through re- 

 moval of obstacles to growth in consequence 

 of some disturbance in the normal relations 

 or equilibrium of the cells with surrounding 

 parts. The capacity to proliferate must be 

 present in the cells, but with the cessation 

 of growth this capacity is rendered latent or 

 potential by the establishment of definite 

 relations or an equilibrium between cells 

 and neighboring parts, iacluding under the 

 latter not only adjacent cells, but also base- 

 ment-substance, lymphatics, bloodvessels, 

 tissue-juices, chemical substances, etc. It 

 is evident that under these circumstances in 

 only two ways can the cells be incited to 

 growth, either by removal of resistance or 

 obstacles to growth, or by an increase in 

 the formative energy resident within the 

 cell, and that in either way energy must be 

 used, whether it be employed to remove 

 obstacles to growth or to increase the pro- 

 liferative forces within the cell. 



It appears to me by no means an easy 

 matter to decide in all cases in which of 

 the two ways mentioned cell-proliferation is 

 brought about. Removal of obstacles to 

 growth, not only in the way indicated by 



Weigert, but also by other disturbances in 

 the neighborhood relations of the part, 

 and very probably by the presence of 

 definite chemical substances, may be the 

 explanation of all pathological cell-growths. 

 Certainly it would not be easy conclusively 

 to disprove this view. Nevertheless, I fail 

 to comprehend the inherent difficulties 

 which some find in admitting the possibility 

 of forms of energy, acting from without, 

 directly increasing the formative energy of 

 the cell ; in other words, directly stimula- 

 ting the cell to growth and multiplication. 

 If such a possibility be admitted, the natural 

 interpretation of some examples of cell- 

 proliferation is that they are directly caused 

 by the action of external forces, in the sense 

 advocated by Virchow. 



Students of the problems of pathological 

 cell-growth must take into consideration 

 not only the facts of human and allied 

 pathology, but also those which are so 

 rapidly accumulating in the domain of ex- 

 perimental embryology and morphology, to 

 the importance of which I have repeatedly 

 referred in this address. I would call 

 attention especially to the observations 

 from this source as to the influence of 

 various changes of environment, particu- 

 larly of definite chemical, thermic and 

 mechanical changes in surrounding parts, 

 upon the direction of movement and growth 

 of cells. The use at present made of chemo- 

 tactic phenomena in explaining the direc- 

 tion of movement of cells in human patho- 

 logical processes is only a very limited and 

 inadequate application of these important 

 observations concerning tactic and tropic 

 stimuli. We shall come to realize more 

 and more the operation of these factors in de- 

 termining cell-movements and cell-growth 

 in human pathology. We already have 

 evidence that different kinds of leucocytes 

 not only possess different specific functions, 

 but also respond in different ways to definite 

 tactic stimuli. The long-standing problem 



