127 



TESTS FOU HYDROGKN SULPHIDP]. 



The tests for HjS were made by suspending in the tops of test tubes, 

 containing cultures of Ps. hyacinthi, narrow strips of filter paper 

 which had l^een dipped in a saturated water solution of c. p. lead ace- 

 tate. The strip was held in place by having its upper end wedged 

 between the wall of the tube and the close»fitting cotton plug. The 

 following trials Avere made: 



(1) Coconut cullure. — Growth good. Paper introduced on fourteenth day. Result: 

 Strip feebly browned in 24 hours. Removed and inserted another moister paper. 

 In 48 hours the lower 1 cm. of the strip was distinctly brown, but not deep brown. 



(2) Coconut cullure {from (mother series). — Growth good. Paper introduced on 

 fourteenth day. Result: Very marked browning of the lead acetate paper in 48 

 hours. After 3 weeks the strip was black in lower one-half inch, and brownish for 

 another one-half inch. The bacterial layer was bright yellow and the substratum 

 unstained. 



(3) Carrot culture. — Growth good. Paper introduced on the ninth day. Strip 

 examined and remoistened on fifth day. Result: No browning of the paper so long 

 as the experiment continued (42 days). Substratum browned. 



(4) Potato culture. — Growth good. Paper introduced on fourteenth day. Result: 

 No browning of strip so long as under observation (3 weeks). Substratum grayed. 

 Fluid feebly browned. 



(5) Rutabaga, culture. — Growth good. Paper introduced on third day. Result: 

 No browning of the lead paper in 47 days. A slow browning of substratum, and 

 bacterial slime. 



(6) White radish culture.- — Growth good. Pajjer introduced on third day. Result: 

 No stain of the strip in 61 days. Substratum browned. 



(7) Yellou) (/lobe turnip culture. — Growth good. Pai:)er introduced on third day. 

 Result: Seventh day, copious growth; no stain of the lead pai>er. Eighteenth day, 

 a slight browning of the strip at bottom and a fee)>le browning of the upper part of 

 the substratum. Twenty-seventh day, a feeble browning of the lower part of the 

 lead paper; distinct pale browning of the upper part of the substratum. Thirty- 

 fourth day, a slow increase of the brown color in the lead paper; slime neutral. 

 Sixty-fourth day, only a slight browning of the lower end of the lead acetate paper; 

 substratum brown (burnt umber); fluid grown full (solid) with yellow-brown 

 slime; reaction acid. 



Conclusion: I*s. hyaclntld caused prompt browning of lead paper 

 when grown on sulphur-bearing sul)strata, which did not stain brown. 

 With one exception, there was no evolution of hydrogen sulphide 

 (browning of lead paper) when grown on substrata which became gray 

 or brown as a result of the growth of the organism, although some of 

 these nui.st have been ver}'^ rich in sulphur compounds. Quer}-: Was 

 the HgS fixed in the substratum as fast as formed, by anunonia, with 

 the resultant brown stain '^ See The Brown Pigment. 



Pa. campestris behaved in much the same way. The lead paper was 

 promptly browned when exposed over cultures on coconut, and the 

 substratum was not stained. Exposed over potato and rutabaga, 

 there Avas no browning of the paper, but a brown .staining of the sub- 

 stratum. Exposed over white radish and 3^ellow globe tiiiiii]), oj 



