EFFECT OF THYROID ON DIVISION OF PARAMAECIUM 309 



In order to secure a conclusive answer to the question whether 

 Paramaecia actually ingested particles of thyroid, the writer 

 performed the following experiment, suggested by the methods 

 employed by M^talnikow ('12). Having stained some particles 

 of Armour's desiccated thyroids with an alcoholic solution of 

 Congo Red, and washed out the free color in distilled water, 

 they were placed in a watch-glass of boiled tap water with sev- 

 eral individuals of Paramaecium caudatum. It was possible to 

 watch the formation in the Paramaecia of gastric vacuoles con- 

 taining these prepared thyroid particles, and, following the cyclo- 

 sis, to observe the change from acid to alkaline reaction shown 

 by the Congo Red as described by M^talnikow. I have perma- 

 nent preparations fixed with osmic acid vapor that show these 

 thyroid filled vacuoles very clearly. 



If then the Paramaecia can and do ingest these thyroid par- 

 ticles and if after ingestion the chemical reactions which are 

 commonly accepted as indicating digestion are observed, does it 

 not follow that the effects produced by the thyroid result only 

 after ingestion and presumably digestion? Certainly this is in 

 accord with Gudernatsch's results. 



The individuals treated with thyroid were as a rule more active, 

 and slightly smaller than the control individuals, and their 

 protoplasm was more transparent. This would be the case if the 

 process of metabolism were accelerated by the thyroid. The 

 thymus treated individuals on the other hand were more slug- 

 gish, larger and darker than the control forms, these appearances 

 apparently being due to large quantities of undigested food gran- 

 ules. The conclusion seems obvious that the effect of the thy- 

 roid is directly upon the metabolic activities of the cell. 



With the effects of the thyroid upon growth and differentiation 

 this investigation is obviously not concerned. 



Returning now to Experiment IX we find the data presented 

 more difficult to analyze. Here the thyroid does not increase the 

 division rate at a time when the control line is losing the power 

 of division and evidently dying cut. Compare this with Ex- 

 periment V, when the control line was also at a very low state of 



