II. 



HISTORICAL REVIEW. 



Xorinal physiology has nearly always tlealL with the 

 investigation of the functions of organ-systems, single organs 

 or certain important cell groups in the bodj^ without 

 going into the study of the physiology of the tissues in 

 general. We must give the pathologists the credit for the 

 initial studies on the various tissues. Up to the present more 

 contributions to the normal physiology of tissues in general 

 have been accomplished by the pathologists. When V i r c h o w 

 created the cellular pathology, new points of view were 

 opened up and new fields for investigations were fertilized. 



The methods of explantation applied in the studies of 

 tissues were very extensively employed in the new cel- 

 lular pathology and many exceedingly important problems 

 were solved. The biology, or general physiology, included 

 mostly the study of the lower organisms, protozoa, etc., 

 but normal physiology made use of the methods of explan- 

 tation too, — mostly however of organ-systems, as for instance 

 the study of the action of the isolated heart, kidney, intes- 

 tines, and so on. But, as already mentioned, the morpho- 

 logical experiments on explanted tissues were actually 

 inaugurated by the pathologists. 



The subjects for investigation by the methods of explan- 

 tation were, to begin with, usually blood cells, egg cells, 

 spermatozoa, ciliated epithelial cells, cells w'hich were easy 

 to isolate and observe in vitro. Later on transparent organs 

 such as the cornea, thin membranes and similar structures 

 were studied in vitro. The experiments of C o h n h e i m 



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