Growth of Mammalian Tissue in Vitro. 477 



unaffected by the presence of any stimulating or inhibiting substance. In 

 the majority of cases two tissues were used, so as to lessen, as far as possible, 

 any experimental errors. A few culUires were made of the spleen, but most 

 of the experiments were carried out with thyroid and liver. These tissues 

 as a rule grow well, and the growth is not obscured by the emigration of cells, 

 as so often happens when spleen is used. 



Young testicular tissue was not cultivated in the present series of experi- 

 ments, for it was considered that, as this tissue only fully develops later in 

 life, false conclusions might be arrived at if the immature testicle of the young 

 rabbit was used. In the majority of cases fresh tissue was made use of, and 

 in this case cross experiments were generally performed, the tissue of young 

 and old animals being grown in plasmata of both animals. A certain number 

 of experiments were conducted with stock cultures of adult testicle which 

 had been growing for ten generations in a medium of plasma and tissue 

 extract. 



(1) Cultivations of Splenic Tissue — 



Experiment 1. — An adult rabbit two years old was anaesthetised. The fur 

 on the ventral surface of the body was removed, the skin sterilised, the 

 carotid artery exposed, and the blood collected in sterile paraffined tubes 

 placed in ice. The blood was then collected from a young animal 10 days 

 old and placed in ice-cold paraffined tubes. Both bloods were centrifugalised. 



The spleen was removed from the young and old animals and placed in 

 Einger's fluid. Four cultures were made of each spleen in each plasma, so 

 that there were four groups. 



At the end of 12 hours there was good emigration of round cells in all the 

 preparations, but it was more marked in the case of the spleen of the young 

 animals both in the young and old plasmata. At the end of 48 hours there 

 was a well marked growth of retiform tissue, which formed mosaic-like 

 masses in the case of the young spleen in the old plasma, but was present 

 in a less marked degree in the case of the old spleen in the old plasma. 

 In both cases such growth was apparently absent when the young plasma was 

 used. 



• Owing to the amount of round cell emigration it was difficult to estimate 

 accurately the extent of the growth, and hence experiments with this tissue 

 were discontinued. 



(2) Ctiltivation of Thyroid and Liver Tissues — 



Eleven experiments, comprising 282 cultivations, were carried out in this 

 group. In all cases both the thyroid and liver were cultivated at the same 

 time. By this means experimental errors were less likely, for if the results 



