EFFECTS OF THYROID ON PARAMAECIUM 



555 



After a few preliminary experiments on the B race had given 

 negative results, the C race was established especially for these 

 experiments. On the whole the results obtained were negative. 

 A few individuals from the th\Toid line formed an abnormally 

 large number of vacuoles in the five minute test : and equally large 

 number formed an abnormally small number of vacuoles. On the 

 whole the averages obtained from the counts of m^any individuals 

 were alike. In table 21 are given summaries of a few of the ex- 

 periments performed on Race C. Here are recorded the period 

 in which the experiments were performed, the number of car- 

 mine filled gastric vacuoles formed in the first five minutes of 

 feeding by the control and thyroid lines, and, for comparison, 

 the percentage increase in division rate produced by the thyroid 

 during the same periods. 



TABLE 21 

 Race C. 'Number of gastric vacuoles formed in the first five minutes of carmine 



ingestion 



This table will serve to show that while there may be an in- 

 crease in the rapidity of gastric vacuole formation in the thyroid 

 fed lines, it is not in the least comparable wdth the increase in 

 the rapidity of division produced. In this connection it will be 

 recalled that whereas Woodruff and Baitsell showed that in- 

 creases in the temperature produced within certain limits in- 

 creases in the rapidity of the division rate directly conformable 

 to van't Hoff's law, Metalnikow studying the effect of the tem- 

 perature on the rate of formation of the gastric vacuoles was 

 unable to bring his results under this same law, the increases in 

 rapidity of vacuole formation being in all cases too small. 



c. On the contractile vacuoles. One of the most striking fea- 

 tures of these experiments was the discovery, in the thyroid fed 

 line of the C race, of Paramaecia with an abnormally large num- 



