104 RHODA ERDMANN 



highly vacuoHzed or fat-storing cells of mesenchymal character 

 with projections at first needle-like and later of a rounded or 

 elongated shape. This twofold manner of development of the 

 bone marrow fat cells is important, as it might probably be the 

 result of a non-uniform origin. 



In judging the transformations of cell types of mesenchymal 

 origin in tissue culture, we already have established certain 

 facts as a basis of comparison. The mesenchymal cells always 

 grow more rapidly than any other known tissue; they have the 

 ability to store fat; they can vacuolize and can emigrate out of 

 the tissue clot. They can endure this highly artificial method of 

 breeding indefinitely. The bone marrow particle, with its loose 

 meshes, exhibits many 'Wundflachen' which are incited into new 

 growth by the stimulus given by the cutting of the tissue. By 

 repeatedly renewing the culture medium and transplantin ; the 

 tissue particle, w^e stimulate the growth again and again, until 

 we have exhausted the power of the network to send newly 

 formed mesenchymelike cells into the plasma, and only a fine 

 thread-like network with a few oblong, small nuclei remains. 

 The pliability of the mesenchymal cell and its ability to undergo 

 transformations is known in embryonic life and is here demon- 

 strated in tissue culture life. 



Two subjects of importance have not been touched. Can 

 these w^andering mesenchymal cells form fibrils, and have they 

 any relation to the formation of the different elements of the 

 bone marrow? Throughout the whole description of the cell 

 transformations in tissue culture, the writer has avoided Foot's 

 conclusion of 1912, namely, since his X cells form fibrils, they 

 must be of the mesenchymal type. The tissue particle of bone 

 marrow has a fibril-forming connective tissue of its own. When, 

 now and then, fibril-forming cells have been seen (as has been 

 the experience of the \\Titer), they may either originate from 

 cells already implanted in the tissue culture, with the bone- 

 marrow particle, or the imbedded fibrils (Foot '12, plate 22, fig. 

 15) may represent fibrils or fibers formed by the fibrin-contain- 

 ing plasma of the culture medium (Baitsell '14, '15). Foot 

 maintains that his X cells form fibrils but he does not prove it. 



