594 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Blastocystis hominis.* — N. H. Swellengrebel has found two cases 

 of the occurrence of '■^Blastocystis " where the presence of Trichomonas 

 or Ghilomastix could be excluded with absolute certainty. Therefore 

 " Blastocystis " cannot be a normal developmental form of either. The 

 size of blastocysts varies greatly ; the larger they grow the smaller 

 becomes the peripheral fringe of cytoplasm. They were never found 

 except when some other parasite was present. It is probable that 

 *' Blastocystis " is not the name of a genus, but of a peculiar form of 

 degeneration to which representatives of different genera of intestinal 

 Protozoa are liable. It is probable that Alexeiff's B. enterocola is 

 different from forms described in man under the same name. 



Race of Paramecium with Extra Contractile Vacuoles. f — Robert 

 T. Hance has studied a race of Faratneciiim cavdatum with two to seven 

 contractile vacuoles. It may possibly have arisen under the influence 

 of high temperatures. The individuals range from 167 fx. to 307 /x, and 

 are unusually strong and resistant. A slightly denser portion extends 

 in some individuals as a band across the middle. The extra vacuoles 

 are generally at the posterior end. The number may increase during 

 the individual lifetime. Various conditions affect the number of 

 vacuoles present in the individual, such as the rate of division and the 

 age of the culture medium. Though extra vacuoles may not appear for 

 several generations for the above reasons, the potentiality is not lost. 

 The division rate ranges between one and five times in twenty-four 

 hours. Besides being influenced by the rate of division the vacuole 

 number may apparently be increased in the individual by the presence 

 of katabolic products in the environment. To heat, cold, distilled 

 water, etc., the resistance of the race is very high. The rate of pulsation 

 of the vacuoles is slightly slower than in the common race, but the 

 power of excretion is greater. 



There is some evidence that conjugation is induced by the concen- 

 tration of katabolic products in the environment. Conjugation has no 

 effect on the new character. 



It may be that a potentiality for extra vacuoles rather than 

 for a definite number is passed on from generation to generation, and 

 that this potentiality is affected by various conditions during the life- 

 time of the individual. Selection has no effect in raising or lowering 

 the vacuole number. The location of the vacuoles in the parent has 

 an immediate but temporary effect on the number possessed by the 

 offspring. 



Effect of Thyroid Diet on Paramecium.! — Waldo Shumway finds 

 that a diet of thyroid substance, either as emulsion of raw thyroids or 

 as a suspension of the commercial powder, produces on Paramecium 

 aurelia or P. caudatum. a constant and significant increase of 65 p.c. in 

 the rate of division over that observed in a hay infusion. The thyroid 



* Parasitology, ix. (1917) pp. 451-9 (2 pis.). 



+ Journ. Exper. Zool., xxiii. (1917) pp. 287-333 (3 pis. and 12 charts). 



X Journ. Exper. Zool., xxii. (1917) pp. 529-63 (12 figs.). 



