DEPARTMENT OF EMBRYOLOGY.^ 



George L. Streeter, Director. 



In preparing this account of the activities of the Department of Embry- 

 ology during the past year, I have grouped the individual investigations under 

 the following headings: (1) Studies on the structure and function of the cell; 

 (2) Studies on the structure and development of individual organs; (3) An- 

 thropological studies on the growth of the fetus; (4) Studies bearing on the 

 physiology of reproduction; (5) Studies on the pathology of the fetus. This 

 classification is, of course, only one of convenience, and it is to be borne in 

 mind that the various studies are closely interwoven and have many contacts 

 with each other. The purpose of all of them, however, is to provide a better 

 understanding of the factors that finally determine the structure of the 

 human body. 



STUDIES ON THE STRUCTURE AND FUNCTION OF THE CELL. 



Heart-Muscle Cells. 

 In my last report I described how Professor W. H. Lewis, by using cultures 

 of liver-tissue, succeeded in isolating living endothelial cells and thus was 

 able to determine the morphological characteristics of that cell type. During 

 the past year he has accomplished the same for heart-muscle. He found that 

 by cultivating chick-embryo tissue in a Locke bouillon-dextrose medium, 

 the heart-muscle cells in about 8 per cent of the cultures migrated out along 

 the cover-glass, where their structure and behavior could be clearly observed. 

 As these cells migrate out they form either an adherent reticulum or an 

 adherent membrane, in which the distinct outlines of the cells can be recog- 

 nized. Dr. Lewis finds here no evidence of a true syncytium, which is in con- 

 firmation of his observations on other tissues. Individual cells in these 

 outgrowths can be seen pulsating, and at rates different from the cells of the 

 explant, the other cells of the reticulum or membrane, and even from the 

 adherent neighboring cells, which proves their physiological as well as mor- 

 phological independence. In accord with the previous observations of Mrs. 

 Lewis, he finds that myofibrils can not be seen in the living cells, but are 

 brought out by fixation. They are thus artifacts in the sense that their 

 appearance is dependent upon the manner in which the contractile substance 

 of the cell is coagulated. The fibrils vary in length and thickness down to the 

 limits of visibility; they may be smooth or cross-striated and in some cells 

 they may be entirely absent, yet all these different cells may have been 

 beating rhythmically before fixation. The myofibrils are never found extend- 

 ing from one cell to another. As another characteristic, Dr. Lewis found 

 that when these cultures were tested for glycogen it was present only in the 



muscle-cells. 



Transformation of Mesenchyme into Mesothelium. 



While studying cultures of heart-muscle cells, Dr. Lewis noted that the 

 multipolar mesenchyme cells which migrate out beneath the cover-glass as a 

 loose adherent reticulum could be observed to change, under the eye, into 

 a flat mesothelial membrane. This striking transformation is accomplished 

 by a partial withdrawal of the long processes and a coincident spreading out 

 of the cytoplasm of each cell until it abuts the cytoplasm of its neighbors in 



^Address; Johns Hopkins Medical School, Baltimore, Maryland. 



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