PROTOPLASM 



of the heart from a chick embryo continued to beat for two to three days after each 

 removal to fresh medium, until unfortunately lost on the 104th day. Embryonic connective 

 tissue could be made into subcultures repeatedly, since it grew so fast. After 14 months, 

 tests grew to 30-40 times their bulk in 5 or 6 days. After 15 months the tissue was still living, 

 although it had been transplanted 172 times. 



It is important to remember that, when isolated tissues grow normally, we 

 have satisfactory evidence of the preservation of their vital activity. 



Some recent experiments by Champy (1913) have given interesting results. 

 Confining our attention, to begin with, to the growth of kidney tissue, taken 

 from an embryo rabbit at full term, we notice certain facts. In Fig. 21, 

 fixed after nine hours of culture, we see a portion of new growth on the right 

 and upper part of the figure, while the cells of the original portion are clearly 

 degenerated ; this degeneration appears to be due to failure of sufficient supply 

 of oxygen. In the new growth there are tubules in the part first formed, but 

 whereas, even in the degenerated state, it is easy to distinguish different kinds 

 of tubules in the original tissue, the new tubules are all alike and of a primitive 

 epithelial type (shown 

 also in Fig. 22). As 

 growth proceeds, we 

 notice that the produc- 

 tion even of these 

 primitive tubules 

 ceases, and there is 

 merely a mass of in- 

 different cells, like those 

 of the embryo before 



tissue differentiation 2ff 



commences. 



If adult tissue is 

 taken, such as smooth 

 muscle, which no longer 

 undergoes cell division 

 in the organism, it is 

 found that mitotic 

 figures are produced 

 in vitro and embryonic 

 cells split off. 



We see thus that 

 differentiated cells, 

 which undergo no 

 further division as long 

 as they are part of a 

 complete organism, when cultivated in plasma outside of the organism, are set off 

 on a course of multiplication, forming cells similar to those from which the 

 differentiated cells were first formed. If it were possible to preserve these cells 

 alive for a sufficient time, it would be extremely interesting to know whether 

 they would ultimately be subject to differentiation into cells similar to those of 

 the tissue from which they grew. 



It seems that cells, when they have taken on special functions in the 

 organism, are normally prevented, by some means, from continuing their 

 primitive multiplication, and that, when this influence which restrains their 

 growth is removed, they start afresh and produce simple embryonic tissue. 

 There is significance in these facts in connection with the formation of malignant 

 tumours. 



The same investigator finds later (1914) that if the fragment of tissue happens 

 to be composed of both epithelium and connective tissue, the new cells growing 

 from the epithelium remain like those from which they grow; whereas, if by 

 chance some of the epithelium leaves the connective tissue and grows towards 

 the outside of the plasma, its cells loose their typical aspect and arrangement, 



FIG. 22. INDIFFERENT RENAL TUBULE FROM THE GROWING 

 ZONE OF A CULTURE SIMILAR TO THAT OF THE PREVIOUS 

 FIGURE. After seven hours. Fixed in Bouin's fluid, 

 stained with iron haematoxylin. 



c, cells arising from connective tissue. 



(Champy, 1913, fig. 5.) 



