1910] on Light Reactions at Low Temperatures 927 



shows the growth in a flask kept vacuous for fifteen days, and then 

 opened to the air. Curve (i) is the growth of a colony in an ordinary 

 open flask, which, however, was exhausted and sealed on the fifteenth 

 day. Curve (ii) is practically a horizontal line during the fifteen 

 days of exhaustion, showing no development of the colony, whereas 

 during this time curve (i) shows a steady increase. After the fifteen 

 days, however, curve (ii) begins to develop, and shows an increase 

 corresponding to the opening of the exhausted flask. The effect 

 of oxygen can be illustrated by a few experiments. This flask 

 contains some broth culture of these bacilli, and is only feebly 

 luminescent, but on bubbling oxygen through the liquid the froth so 

 formed is exceedingly bright, the bacteria being excited by the oxygen 

 to great activity. Here are three flasks over the interior surface of 

 which some phosphorescent culture medium has been spread, followed 

 by exhaustion of the flasks. They have remained so for one, two, 

 and three weeks respectively. Upon opening these flasks the 

 luminescence will once more re-establish itself by the action of the 

 oxygen so admitted, although (especially in the case of the three 

 weeks' old culture) its full brightness will not develop for 24 hours. 

 The phosphorescent bacteria behave differently towards various 

 metals. Various cultures have been prepared, and plates of various 

 substances placed thereon, and remarkable effects obtained. Some 

 reproductions of these are shown (Plate V. figs. 1 to 6). Thus, a 

 disk of zinc caused death to the organisms in a considerable zone 

 surrounding it. Similarly, also, copper and silver, and especially 

 mercury, which is particularly fatal. Tin, on the other hand, is 

 inactive. 



A piece of the metal whose effect it is desired to examine is placed 

 in the centre of the tin dish containing the medium infected with 

 the phosphorescent bacteria. The growth of the phosphorescence is 

 then observed. Several metals have no apparent effect. Among these 

 are gold and the platinum group, tantalum, cadmium, magnesium and 

 tin. Similarly coconut charcoal, graphite, and selenium have no 

 effect. Sulphur seems actually to stimulate the bacteria which cluster 

 brilliantly round it on the culture, leaving the rest of the plate rela- 

 tively dark. The metals which have been found to slightly check 

 the growth in their neighbourhood are bismuth, thallium, lead and 

 nickel. The alloys German silver, hard brass, and aluminium bronze 

 have also only a slight effect. A stronger action is shown by iron, 

 aluminium, zinc, copper and soft brass. The more deadly metals are 

 cobalt, silver, mercury, antimony, arsenic, and phosphor bronze. 

 Chloride and bromide of silver, cyanide of mercury, and arsenous 

 acid also kill the bacteria. The destructive effect of the metal clearly 

 depends on its slow solution at the ordinary temperature in the 

 saline organic culture medium, aided no doubt by the presence of 

 atmospheric oxygen in some cases. 



The following table gives a list of the metals used and their 

 effects on the bacterium. 



YOL. XIX. (No. 104.) 3 P 



