A HISTORY OF SCIENCE 



was needed to demonstrate that the tissues of an in- 

 flamed part become red and swollen; and numerous 

 other changes of diseased tissues are almost equally 

 patent. But this species of knowledge, based on 

 microscopic inspection, was very vague and untrust- 

 worthy, and it was only after the advent of the per- 

 fected microscope, some three-quarters of a century 

 ago, that pathological anatomy began to have any 

 proper claim to scientific rank. Indeed, it was not 

 until about the year 1865 that the real clew was dis- 

 covered which gave the same impetus to pathology 

 that the demonstration of the germ theory of disease 

 gave at about the same time to etiology, or the study 

 of causes of disease. This clew consisted of the final 

 demonstration that all organic action is in the last re- 

 sort a question of cellular activities, and, specifically, 

 that all abnormal changes in any tissues of the body, 

 due to whatever disease, can consist of nothing more 

 than the destruction, or the proliferation, or the al- 

 teration of the cells that compose that tissue. 



That seems a simple enough proposition nowadays, 

 but it was at once revolutionary and inspiring in the 

 day of its original enunciation some forty years ago. 

 The man who had made the discovery was, a young 

 German physician, professor in the University of Frei- 

 burg, by name Rudolph Virchow. The discovery 

 made him famous, and from that day to this the name 

 of Virchow has held somewhat the same position in the 

 world of pathology that the name of Pasteur occupied 

 in the realm of bacteriology. Virchow was called 

 presently to a professorship in the University of Berlin. 

 In connection with this chair he established his fa- 



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