Tissue in Autogenous and Homogenous Plasma. 457 



of the inhibitory substance, therefore a certain amount of growth takes 

 place in fresh plasma. In plasmata which are not " good " only a small 

 amount of growth takes place when the plasma has been frozen for 

 three days. This is not so easy to understand ; it may be that the 

 stimulating substance is present in a less marked degree, and is therefore 

 all destroyed at an earlier date, so that after the plasma has been frozen 

 for three days there will be little or none present, hence growth will be 

 slight or absent. It was noticed, however, in the cases above where growth 

 was slight that coagulation of the plasma had been incomplete ; in some 

 cases, indeed, the plasma had remained quite liquid, so that there was 

 risk of the tissue washing off the slide. It is possible therefore that failure 

 to grow under such circumstances was due to mechanical factors, the 

 plasma failing to form a scaffolding for the growing cells. It is of interest 

 to note that the plasma which failed to coagulate was not serum, for there 

 was no clot present when the frozen material was thawed. 



Thyroid. 



Of this tissue 167 cultures were made, the experiments being carried out 

 on similar lines to those described for the testicle, but a larger number of 

 cultures were made, so that the plasmata were compared at shorter intervals 

 of time. 



Experiment 6. — Homogenous plasma was removed one day previous to the 

 cultural experiment and frozen. Autogenous plasma was removed from the 

 animal at the time of the experiment and cultures of thyroid tissue made 

 in each plasma under identical conditions. Growth was more marked in 

 the homogenous plasma and a greater number of cultures were positive in 

 this. 



Experiment 7. — Thyroid tissue was cultivated in eight days' old homo- 

 genous plasma and in fresh autogenous plasma. There was no growth in 

 the homogenous plasma, whereas in the fresh autogenous plasma 42 per 

 cent, of the cultures grew and the amount of growth was well marked. 



Thus, as in the case of the testicle, growth is better in plasma that has 

 been preserved for one day, but entirely ceases in plasma which has been 

 frozen for eight days. 



In the next series the same plasmata were used for several experiments, as 

 in the case of the testicle, so that any given plasma which was autogenous in 

 one experiment became homogenous in the next, and had been kept frozen 

 for periods of time which increased for each successive experiment. 



Experiment 8. — Thyroid tissue was cultivated in fresh autogenous plasma 

 and in the plasma used in Experiment 7, which was now five days old. 



2 M 2 



