132 THE BIOLOGY OF STENTOR 



are unable to consummate regeneration. Improper healing of cut 

 animals is supposed to offer a blockage to regeneration according 

 to Sokoloff (1924) and Weisz (1948a) ; but my experience is that the 

 healing capacity of stentors is sufficient for neat repair after any 

 cutting operation except an extreme reduction in the ectoplasm 

 which alone prevents apposition of cut surfaces. 



Nevertheless regeneration can be blocked in Stentor by treat- 

 ment with certain chemical agents. Weisz (1955) tested the effects 

 on regeneration of over 20 compounds, including substituted 

 purines and pyrimidines and a variety of anti-metabolites. The 

 most effective, in the sense of producing reversible blockages 

 without toxicity, was acriflavin, a mixture of 2,8-diamino-io- 

 methyl-acridinium chloride and 2,8-diamino-acridine. These 

 compounds or their allies are bacteriostatic, and some of their 

 effects on ciliates had already been explored (Robertson, 1925). 

 Weisz reported that acriflavin has a graded sequence of effects on 

 coeruletis, depending on concentration and duration of exposure. 

 First there was some paralysis of ciliary beating and cell contrac- 

 tion, followed by more or less complete shedding of the peUicle. 

 Oral primordium formation might then be merely delayed, or pre- 

 vented entirely, the animals then dying. When primordium forma- 

 tion occurred there were graded effects in the completeness of the 

 development of the anlage. The primordium might appear briefly 

 and then be resorbed without any attempt at re-regeneration. Oral 

 formation might be arrested at stage 4, producing a membranellar 

 band which developed no further. Sometimes the band could 

 assume the normal curvature but failed to coil inward and develop 

 the gullet and associated mouthparts. These inhibitive effects 

 could be reversed or counteracted by other agents: adenine, 

 guanine, thymine, uracil, folic acid, RNA, and DNA, the two 

 latter, presumably the commercial product from yeast, being the 

 most effective. Interpreting these findings, Weisz postulated that 

 development of the oral primordium is a series of separate morpho- 

 genetic events interconnected by acriflavin-sensitive transition 

 reactions. Kinetosomes might be affected in several of their 

 functions, first in the promotion of ciliary beating, then in their 

 synthesis of new cilia, and finally in some morphogenetic activity 

 by which membranelles and other complex organelles are pro- 

 duced. Application of compounds which reversed the effect of 



