41 



Table VIII. 



prod. I 

 5. niberbalt. 

 S. ruber miq. 

 J. rutilus (n. sp.) 

 5. amylor. (n. sp.) 

 5. rosac. metali. 



+ + 

 + 4- 

 + + 

 4- + 



pink 

 pink 

 pink 

 pink 

 f red 



10 days' growth after exposure to sun 



prod. I 

 ruber bait, 

 ruber miq. 

 rutilus (n. sp.) 

 amylor. (n. sp.) 

 rosac. metali. 



48 hours after 2 hours exposure to sun. 

 Growth normal, pigment faint pink 



thin, faint pink 



very slight, slight 



normal, faint pink 



thinner normal 



no development 



From the tables it will be seen that the 24 hour cultures pre- 

 sented a curious developmental result. The cultures of B. ruber 

 balticus which had been made after 30 minutes' exposure to the 

 sun showed more development than the control, while the other 

 exposures exhibited a comparative decrease of effect, a 5 minutes' 

 exposure giving less growth than one of 15 minutes. Greater 

 development of a 15 minutes' exposure as compared with one of 

 5 minutes was also shown by B. prodigiosus, B. ruber miquel, 

 and B. amyloruber, so that the possibility of an accidental 

 mechanical error, e. g., the transference of a loopful of germs crowded 

 at one side of the tube by heliotaxis, was excluded from consideration. 

 The experiment was repeated for B. ruber balticus, B. 

 rutilus, and B. amyloruber with the same results. 



A possible explanation of the phenomenon may be suggested. 

 Gotschlich (5) has remarked that brief exposure of a culture to 

 an injurious influence may react beneficially to the culture as a whole, 

 by cutting out the weaker organisms, and leaving only the u Aus- 

 nahmezellen" ; that is, that there may be selective death-rate. On this 



