September 19, 1902.] 



SCIENCE. 



443 



wor.ds that every cell is derived from an- 

 other cell. No matter how much the forms 

 of the cells may vary, every new form is 

 derived from a previous form. Cells, in 

 the course of their lives, may change their 

 forms according to age and according to 

 the influences to which they are subjected. 

 Such changes take place both in the healthy 

 and in the sick organism, and often it is 

 impossible to draw a sharp line between 

 normal or physiological, and abnormal or 

 pathological, changes. Virchow himself ex- 

 presses these views in the words that in 

 reality there is no distinct line of demar- 

 cation between physiological and patholog- 

 ical processes, that the latter are only phys- 

 iological processes which take place under 

 difficult conditions. The cell which changes 

 its form during its lifetime may, there- 

 fore, be said to be variable ; or, in Virchow 's 

 words, it possesses mutability. From his 

 point of view the whole question of the ori- 

 gin of species centers in the problem of the 

 relation between the mutability of the or- 

 ganism and the mutability of the cell. 

 The comparison of the forms of organisms 

 and organs may form the starting point of 

 researches on variability, but the study of 

 the variations of the whole organism or or- 

 gan must be based on the study of the vari- 

 ations of the constituent cells, since the phys- 

 iological changes of the whole body depend 

 upon the correlated physiological changes 

 that take place in the cells. Without a 

 knowledge of the processes that take place 

 in varying cells, it is impossible to deter- 

 mine whether a deviation from the normal 

 form is due to secondary causes that af- 

 fect during their period of development or- 

 gans already formed, or if it is due to pri- 

 mary deviations which develop before the 

 first formation of the varying organ. 



Two questions, therefore, arise : the first, 

 if secondary deviations may become hered- 

 itary. For this no convincing proof has 

 been found. The second question is 



whether primary variations do occur, and 

 if so, whether they are hereditary. 



Led by these points of view Virchow de- 

 mands that researches on the origin of spe- 

 cies be based on researches on the mutabil- 

 ity of cells and groups of cells, and he de- 

 clines to speculate on the origin of species, 

 until through researches on tissues a sound 

 foundation has been laid. Sometimes it 

 would seem as though Virchow doubted the 

 scientific value of the theory of evolution. I 

 do not think this is the case. He merely em- 

 phasizes again and again the methodolog- 

 ical point of view, that the understanding 

 of the forms of the body must be based on 

 a knowledge of the forms, mutual relations, 

 and functions of the cells and that, there- 

 fore, the question of 'mutability' must be 

 settled by researches on these lines. 



Furthermore his position rests on the 

 general scientific principle that it is dan- 

 gerous to classify data that are imperfectly 

 known under the point of view of general 

 theories, and that the sound progress of 

 science requires of us to be clear at every 

 moment, what elements in the system of 

 science are hypothetical and what are the 

 limits of that knowledge which is obtained 

 by exact observation. To this principle Vir- 

 chow has adhered steadfastly and rigidly, 

 so much so that many an impetuous stud- 

 ent has felt his quiet and cautious criticism 

 as an obstacle to progress. On this account 

 he has suffered many hostile attacks— until 

 generally the progress of research showed 

 that the cautious master was right in re- 

 jecting the far-reaching conclusion based on 

 imperfect evidence. There are but few 

 students who possess that cold enthusiasm 

 for truth that enables them to be always 

 clearly conscious of the sharp line be- 

 tween attractive theory and the observation 

 that has been secured by hard and earnest 

 work. 



There are two anthropological problems 

 which are important in their relation to the 



