1893.] 



Pathology among Biological Studies. 



127 



to Brown's theory neither a positive nor a negative value. Johannes 

 Muller rescued for general physiology, in which it has ever since kept 

 its place, that which was valuable in Brown's system, the doctrine of 

 the integrating life stimuli. The occasional stimuli which produce 

 disease have found their place in etiology ; their significance has 

 become more and more sharply defined, the more accurately we have 

 learnt to distinguish between the causes and the essences of disease, 

 a distinction which became more difficult as the "causae vivae" of 

 diseases became known in ever-increasing numbers. And now a new 

 task has arisen, namely, to draw into our sphere of observation the life 

 of the causative agents themselves. 



The way in which pathology has tried to approach the desired 

 goal, to fathom the living substance in its diseased conditions^ 

 has led us a great step forward. Pathological anatomy, especially, 

 has opened this road. The more numerous its observations, and 

 the more it penetrated into the details of the lesions, the smaller 

 became the field of so-called general diseases. The first steps of 

 mediaeval anatomists had the effect of drawing the attention 

 to local diseases. In the first and longest period, which we 

 may define as that of Regionism, the pathological anatomists 

 sought the cause of disease in one of the larger regions or cavities of 

 the body — in the head, chest, or abdomen. In the second period, 

 ushered in by the immortal work of Morgagni, shortly before the 

 time of which I last spoke — the time of Brown and Hunter — they 

 endeavoured to find in a certain region the actual organ which might 

 be considered as the seat of disease. On this foundation arose the 

 Parisian school of Organicism, which, until late in this century, held 

 a dominant position in pathology. In this school, already, they 

 recognised that not the organ, nor even a portion of it, could be the 

 ultimate object of research. Xavier Bichat divided the organs into 

 tissues, and showed that in the same organ sometimes one and some- 

 times another tissue might be the seat of disease. 



From that time forward the eye of the pathological anatomist was 

 directed chiefly to the changes in the tissues, but it soon became 

 apparent that even the tissues are not simple substances. Since 

 the third decade of this century, the microscope has disclosed the 

 existence of cells, first in plants, and very soon afterwards in animals. 

 Only living beings contain cells, and vegetable and animal cells show 

 so much similarity of structure that one can demonstrate in them the 

 actual product of organisation. This conviction has become general, 

 since through our embryologists, especially through Schwann, proof 

 has been afforded that the construction of embryonic tissues is 

 derived from cells both in the highest animals and in man himself. 



In the fourth decade of this century the science of pathological 

 anatomy had already begun to be directed towards cells. These re 



