RESEARCH IN MEDICINE 553 



tions (1839-1843) which he brought forward was able to formulate a 

 definite cell theory for plants; later when this theory was applied to 

 animal tissues and developed by Schwann and Virchow it became an 

 influence as great as that of the theory of evolution, in the development 

 of modern biology. 



Schwann, who was at the time an assistant of Miiller, received di- 

 rectly from Schleiden the impulse to compare animal and vegetable 

 cells. ^Yhi[e carrying out for Miiller the experimental study of nerve 

 and muscle, necessary for the proper preparation of his chief's great 

 book on physiology, he became interested in the histological study of 

 these structures and it was at this time that he described the nerve 

 fiber sheath which now bears his name. Once, when he was dining with 

 Schleiden in 1837, the conversation turned to the nuclei of vegetable 

 cells, Schleiden's description of these recalled to Schwann similar 

 structures which he had seen in animal tissues. The resemblance be- 

 tween the animal and plant cells was, without loss of time, confirmed by 

 both observers and the result was Schwann's famous paper (1839) on 

 the accordance in structure of animal and plant tissues. 



It is difficult for the student of to-day, thoroughly drilled concern- 

 iiig the details of cell structure in his courses in normal and pathological 

 histology, to realize that only a little over 70 years ago the essential 

 feature of the animal cell, the nucleus, was not recognized, and that it 

 was a botanist who first brought the subject to the attention of a physi- 

 ologist. Medicine in all its phases has advanced rapidly along the path 

 thus opened up by Schleiden and Schwann. To-day we are interested 

 above all other things in the chemistry of the cell, but from the time of 

 Schwann to the time of Pasteur the study of the morphology of the cell 

 in health and in disease was one of the chief interests of scientific 

 medicine. 



It is not to be supposed, however, that Schwann had the conception 

 of the cell which we have to-day. He, as Schleiden before him, made 

 faulty observations and drew faulty conclusions. The important fea- 

 tures of Schwann's work were the recognition of the nucleus, not the 

 cell wall, as the important part of the cell, the demonstration of the 

 union or grouping of the cells to form tissues,- and the demonstration 

 that the distinctive cells of the tissues of the adult develop from the 

 undifferentiated cells of the early embryo. The misconceptions of the 

 early histologists were natural when we recall the great technical diffi- 



^This statement does not disregard the work of Bichat (1771-1802), fre- 

 quently called the "father of histology," to whom is due the credit of first 

 recognizing the fact that the body was made up of distinct and differing tissues. 

 Bichat 's results, however, were obtained by the use of chemical reagents. He 

 used the microscope but little, and his work, important as it was, and antedating 

 the cell theory by 40 years, can not be considered as leading to the development 

 of the cell theory. 



VOL. liXxx. — 37. 



