Growth of Mammalian Tissue in Vitro. 



479 



itself evidence of value of the suitability of the media and the power of the 

 tissue to grow. The results of these experiments may be summarised as 

 follows : — 



(a) Young Tissues Growing in Old Plasma. — It was found that growth was 

 in all cases extensive and successful. Cultivations occurred in 100 per cent, 

 of the cases. 



With the thyroid, masses of cuboidal cells were seen extending into the 

 plasma, and between them were large numbers of branching connective 

 tissue cells. 



In the case of the liver, the growth was also extensive, and after 48 hours 

 large masses of the characteristic deeply staining cuboidal cells were visible 

 together with large numbers of connective tissue cells (fig. 1). Successful 

 results were again obtained in 100 per cent, of the cases. In both groups 

 the growth continued for four or five days before any signs of degeneration 

 occurred. 



(b) Young Tissues Growing in Young Plasma. — With this group there was 

 a very marked difference. There is considerable difficulty in obtaining the 

 blood of these young animals, owing to their small size, and it was at first 

 thought possible that the difference in growth might be due to the fact that 

 the plasma so obtained was not in good condition. It was found, however, 

 that the results were practically constant even after these difficulties had 

 been overcome. 



In the case of the thyroid only 8 per cent, of the specimens showed any 

 growth, and they were thus sharply differentiated from the specimens of the 

 same tissue growing in old plasma. Even in those cases in which the 

 growth was present it was slight in amount. In no case were any cuboidal 

 cells seen, and even after three or four days there were only present a few 

 connective cells growing from scattered areas at the edge of the tissue. This 

 result was constant apart from liquefaction of the plasma, which in other 

 cases has been found to limit growth. That is to say, the decrease in growth 

 did not appear to be due to mechanical causes. 



With the liver similar results were obtained. In this case a larger number 

 of the preparations showed growth, the results being positive in 26 per cent, 

 of the cases. In one specimen (Experiment 5) there was very good growth, 

 but in three other specimens of the same series there was no growth, and 

 such a result did not occur again in the other series. It is probable, theie- 

 fore, that this result was an experimental error. In the remaining 

 specimens which showed growth the extent of the growth was slight. In 

 some cases a few outgrowths of cuboidal deeply staining cells were seen, but 

 in no case were they so extensive as when old plasma was used as a medium. 



