THE BIOLOGY OF MICROBES, ETC. 135 



the surface of the nourishing medium (Fig. 34). The 

 green pigment is soluble in alcohol, and an alcoholic 

 solution gives an absorption spectrum, consisting of 

 a band extending from the extreme violet to the 

 blue part (nearly to the Fraunhofer line F) of the 

 spectrum. There is also an absorption band in the 

 green, and one in the yellow, part of the spectrum. 

 The end of the band in the yellow is exactly in the 

 same position as the D line in the solar spectrum. 

 Bacterium allii forms an alkaloid or ptomaine from 

 albuminoid molecules. This ptomaine has the same 

 chemical composition as hydrocoridine (C 10 H 17 N). 1 

 Besides the pigment and ptomaine, small quantities 

 of sulphuretted hydrogen gas are liberated from the 

 medium on which the microbe lives. The sulphu- 

 retted hydrogen was proved by the black stain (PbS) 

 produced upon paper impregnated with a solution of 

 lead acetate, and also by the yellow stain (CdS) 

 produced on cadmium paper (CdCl 2 ). B. allii is 

 best stained with gentian violet. The vitality of 

 this microbe is remarkable, 2 for it still retains its 

 vitality when exposed, in a dry state, to a tempera- 

 ture of 32 C. for six months. A pure culture of 

 this microbe exposed to 15 C. for three days 

 proved that it was not killed ; but it was killed 

 after fourteen days' exposure at the same tempera- 

 ture. An E.M.F. of 3 -3 volts killed B. allii iii ten 

 minutes. 



1 See Dr. Griffiths' papers in Comptes Rendus de I'Acade'mie 

 des Sciences, tome 110, p. 416 ; and Gentralblatt fur Bakte.riologie 

 und Parasitenkunde, Bd. vii. (1890), p. 808. 



- Proceedings of Royal Society of Edinburgh, vol. xvii. pp. 

 262-264. 



