1909.] Hillhousia mirabilis, a Giant Sulphur Bacterium. 



401 



difficulty. The culture should now be shaken up at intervals, and very small 

 quantities of sulphuretted hydrogen water added every few days. 



Such a culture will thrive for a time, although the multiplication of the 

 organism is relatively very slow. 



The organism thrives best when the flocculent organic matter, after 

 straining, is allowed to remain in the water. Under these circumstances the 

 bacterium remains healthy, and can be kept for a very long time without any 

 addition of sulphuretted hydrogen water. 



Experiments in obtaining pure cultures are still proceeding, and discussion 

 of this part of the investigation is for the present deferred. 



Keeping the organism in the original mud in which it is collected, without 

 constant change of water, proves unhealthy and ultimately fatal. This is 

 due to the accumulated excess of sulphuretted hydrogen in the water, which 

 causes the bacteria to lose their sulphur. The addition of a strong solution 

 of sulphuretted hydrogen to a culture also causes a solution of the sulphur 

 and the death of the organisms. 



Light is unnecessary for the perfect growth of this bacterium, cultures 

 thriving as well in complete darkness as in diffuse light. 



In mass and by reflected light a culture presents a greyish-white 

 appearance. 



Cytological Structure. — Formalin has been found the most useful fixing 

 reagent on account of the fact that the sulphur globules are removed at the 

 same time. A 2^-per-cent. solution of commercial formalin will completely 

 remove the sulphur in the course of a few hours.* 



Individuals fixed in this way show a network of protoplasm which occupies 

 the interstices between the sulphur globules, the position of the latter being 

 indicated by the large clear spaces (figs. 5 and 19). Embedded in the 

 protoplasmic network are numerous minute granules of very variable size. 

 (These are well shown in fig. 19.) 



The cell-wall is highly resistant to reagents, but becomes much more 

 permeable after the organism has been dried. It contains no cellulose, and 

 stains yellow on the addition of iodine. It dissolves only with difficulty in 

 sulphuric acid, does not dissolve in an ammoniacal solution of cupric 

 hydrate, and in many ways it is suggestive of fungus-cellulose. Its great 

 resistance to reagents is probably due to the presence of a considerable 

 proportion of chitin. 



On the addition of 5-per-cent. carbolic acid to the living organisms, the 

 cell- wall swells up and becomes lamellose, indicating that it is not of 



* The removal of the sulphur is probably brought about by the small quantity of free 

 formic acid present in commercial formalin. 



