DEVELOPMENT OF CONNECTIVE-TISSUE FIBERS. 49 



cells of the tissue to be studied and placing them in a hanging drop of unmiotic 

 fluid. Although he did not obtain any growth of the teased-out cells, he was 

 able to observe the connective-tissue fibrils in connection with the cells throughout 

 the different stages of the development of the connective-tissue fibers, and he 

 became convinced, by this study of the living cells, that the fibrils had their origin 

 within the cells and continued through the exoplasm of one or more cells. Boll 

 studied carefully the following tissues : 



Arachnoid of chick embryo of 4 to 19 days' incubation. 

 Subcutaneous tissue of chick embryo of 7 to 17 days' incubation. 

 Cornea of chick embryo of 4 to 21 days' incubation. 

 Tendon of chick embryo of 7 to 21 days' incubation. 



He concluded that in all of these tissues the connective-tissue fibers originated 

 from the cells. 



In the study of the connective tissue by the tissue-culture method, prepara- 

 tions such as those studied by Boll were used, and also many others, in which 

 the tissue was either teased out, or flattened out, or suspended in a hanging drop 

 of Locke's solution instead of amniotic fluid. Figures similar to those given by 

 Boll were frequently observed (plate 1, figs. 2, 4, and 5), and his observations were 

 corroborated. However, in all such preparations it is impossible to eliminate the 

 possibility of fibrin or some other intercellular substance taking part in the forma- 

 tion of the fibrils, and for this reason these observations will not be given below, 

 although they undoubtedly show the connection of the fibrils with the cells. 



As no cultures containing fibrin have been studied, nothing can be said at 

 this time in regard to Baitsell's observations (1915), by means of which he shows 

 that certain fibers which resemble the connective-tissue fibers may form in a 

 fibrin clot in the presence of a piece of tissue of a chick embryo after various 

 periods of time. In the development of the embryo there can be no question 

 of fibrin playing any part in the formation of the fibrous tissue, since, so far as is 

 known, fibrin is not present in the uninjured tissue. Whether the cells of the 

 embryo possess the power of secreting a substance which may act in the same 

 manner as the injured cell to produce the formation of fibrin, or whether the 

 connective-tissue cells in the developing embryo act directly upon the plasma, 

 are questions which Baitsell does not discuss. He quotes the following experi- 

 ments of Loeb, from Adami: 



"When a drop of uncoagulated lymph is placed between two glass slides, the mere 

 act of pulling one slide over the other leads to the appearance of fibrils, which grow in 

 length and bulk; which like those of connective tissue are not only intracellular, but 

 actually traverse cell bodies situated in their path; which show themselves first in im- 

 mediate connection with the cells, the cells as we now hold liberating an enzyme that 

 determines the modification of the more soluble protein into a precipitated or coagulated 

 modification. But the lines of the precipitation are evidently along the lines of strain." 



These experiments of Loeb are in a way comparable to those of Baitsell, 

 except that in Baitsell's experiments the strain is brought about by the shrinkage 

 of the plasma clot. It seems rather difficult to draw any conclusions in regard 



