492 FOOD REQUIREMENTS 



patently requires thiamine, or both pyrimidine and thiazole. Accord- 

 ingly, Lwoff has concluded that this species is capable of synthesizing 

 this growth factor from the two components, although such a synthesis 

 has not been demonstrated. With respect to growth-factor requirements, 

 A. castellanii thus seems to resemble Polytomella caeca and Chilomonas 

 Paramecium. 



So far, only a few investigations have been completed on the ciliates. 

 Hall and Elliott (1935) noted that the addition of yeast extract in low 

 concentration to a gelatin medium would support growth of Colpidium 

 campylum and C. striatum, whereas gelatin medium alone was unsatis- 

 factory. A. Lwoff and M. Lwoif (1937) have since found that Glau- 

 coma piriformis will grow in a silk-peptone-dextrose medium containing 

 thiamine, while the control cultures failed in the second or third transfer. 

 Likewise, Elliott (1937a, 1939) noted a marked acceleration of growth 

 in C. striatum when thiamine was added to a standard peptone solution 

 and to a peptone medium autoclaved at pH 9.6. In the latter case, the 

 controls showed very little growth in the first transfer. Observations of 

 the Lwoffs (1937, 1938) indicate that G. piriformis requires the entire 

 thiamine molecule, and is presumably unable to synthesize the substance 

 from the thiazole and pyrimidine constituents. Various other related 

 compounds cannot be substituted for thiamine. 



Other Growth V actors. — Vitamin B2 (riboflavin) apparently will not 

 replace thiamine in meeting the growth requirements of Colpidium 

 striatum, although a moderate acceleration of growth by this factor has 

 been noted (Elliott, 1939). A vitamin B,; concentrate has produced even 

 less noticeable effects on the growth of the same species (Elliott, 1939). 



Vitamin C (ascorbic acid) requirements have been investigated in 

 several species. M. Lwoff (1938a, 1939) has reported that ascorbic 

 acid is one of the factors essential to growth of Trypanosoma cruzi, 

 Leishmania tropica, and L. donovani in cultures; and Cailleau (1938a, 

 1938b, 1939) has reached the same conclusion for Trichomonas foetus, 

 Eutrichomastix coluhrorum, and T. columbae. 



Nicotinic acid and nicotinamide both seem to serve as growth factors 

 for certain bacteria (for review, see Koser and Saunders, 1938). None 

 of the investigations on Protozoa has yet been completed. 



Hematin has been found essential for the growth of certain Tryp- 

 anosomidae — for example, Trypanosoma cruzi, Leishmania donovani, 



