LIFE OUTSIDE OF ORGANISM CARREL AND BURROWS. 579 



tain embryonal tissues, which grow rapidly, die early, while the cul- 

 tures of peritoneum and of cartilage, which develop slowly, may re- 

 main in excellent condition for 20 or 25 days. The growth of the 

 culture is often very active. From the surface and the peripheral 

 part of the fragment a great many cells wander out and radiate 

 through the medium. They often form a new tissue around the 

 original fragment. The surface covered by the new cells may be very 

 large. In a culture of spleen artificially stimulated this surface was, 

 after 27 hours, almost equal to forty times the surface of the original 

 fragment. 



The morphologic characters of the culture vary according to the 

 nature, epithelial or connective, of the tissues. The growth of con- 

 nective tissue cells was observed mainly in the cultures of spleen, 

 cartilage, and thyroid. The connective tissue cells do not give rise 

 generally to a continuous layer, as we have observed the cells of the 

 epidermis to do. They invade the medium either as isolated single 

 cells or in rows or chains of cells. Ultimately their processes unite to 

 form an open network. In the cultures of peritoneum the cells may 

 tend for a few days to form continuous layers that spread from the 

 fragment into the plasma. But sooner or later, the rate of growth 

 increases, the continuous layer is dislocated, and after about two 

 weeks the cells spread isolatedly through the medium. In the cul- 

 tures of spleen the cells can conglomerate around a cotton thread 

 and cover it by a layer having the appearance of an endothelial 

 membrane. The cells are fusiform or multipolar. Their cytoplasm 

 is finely granular, while the nucleus appears as a clear spot, contain- 

 ing one or several nucleoli. In the cultures of Rous sarcoma and of 

 the sarcomata of Ehrlich and Jensen, we have observed many differ- 

 ent types of connective tissue cells. Often they possess amoeboid 

 movements. Sarcomatous cells, inoculated to a culture of the an- 

 terior part of the eye of a fetus of chicken, were observed wandering 

 through the pigmented cells and absorbing their dark granules. 



The growth of epithelial tissue was studied chiefly in the cultures 

 of thyroid, kidney, skin, and carcinoma. The thyroid cells are 

 polygonal in form and appear somewhat later than the fusiform cells. 

 They present less distinct outlines and a finely granular protoplasm 

 surrounding a large clear round nucleus, which in turn contains one 

 or two opaque nucleoli. These cells differ from the others in remain- 

 ing in a community and not wandering separately into the medium, 

 and in producing sometimes tubular formations and sometimes con- 

 tinuous layers. Moreover, these cells grow from the edges of the frag- 

 ment as far as the upper surface and in a single plane. In one in- 

 stance, the tubular proliferation was traced to the circumference of 

 a thyroid vesicle which formed its base. In some instances the 

 growth was cup shaped, and later budding occurred, so that rami- 



