1909.] Hillhousia mirabilis, a Giant Sulphur Bacterium. 



403 



partly disappeared, the granules had the appearance of highly refractive beads 

 strung on fine threads (fig. 20). 



The above tests, taken collectively, furnish evidence which goes far to 

 prove that a considerable proportion of the granules present in the general 

 protoplasmic network consist of nucleo-proteids. 



Lastly, the bacterium was tested for phosphorus. A considerable quantity 

 of a culture (pure except for very minute grains of silica) was incinerated on 

 platinum foil, and kept at a red heat for several minutes. The ash was then 

 treated in small tubes with a reagent consisting of 10 c.c. of nitric acid to 

 1 gramme of ammonium molybdate, and kept at a temperature of 50° C. for 

 a week, after which period numerous minute crystals of an intense yellow 

 colour were present in all the slides prepared. These crystals belong to the 

 cubic system, and there is every reason to regard them as crystals of 

 ammonium phospho-molybdate. Slides of the reagent only, kept for the same 

 period at 50° C, showed no trace of such yellow crystals. 



From this test we conclude that phosphorus is present in the bacterium, 

 and therefore that some nucleo-proteid is present.* The previous tests 

 indicate that this nucleo-proteid is in the form of small granules in the 

 protoplasmic network, and the staining proves the granules are not particles 

 of chromatin. 



Thus, Hillhousia is a very primitive unicell in which chromatin has not been 

 developed, and the particles of nucleo-proteid {possibly of the nature of linin) are 

 scattered, evenly through the whole protoplasmic network of the cell. 



Although the cytological structure of Hillhousia can be studied with 

 comparative ease, it must not be assumed that other and less easily investi- 

 gated bacterial cells have a similar structure. The sulphur bacteria may be 

 of a low type, and it is quite probable that among the various known 

 groups of the Schizomycetes there are bacteria in which the cytological 

 structure is of a somewhat higher order. 



The present investigation is only of a preliminary character, as much work 

 yet remains to be done in obtaining pure cultures, and in further working out 

 the cytology of the organism. 



Summary. 



Hillhousia mirabilis is a sulphur bacterium of giant proportions, and is 

 much the largest solitary bacterium which has so far been discovered. Its 

 average length is about 60 /x and breadth about 26 fi. 



The organism is a peritrichous bacterium with a large number of short 



* Galeotti (in ' Zeitschr. fur physiol. Chemie,' vol. 25, 1898, p. 48) has definitely 

 demonstrated the occurrence of a nucleo-proteid in certain bacteria. 



VOL. LXXXI. — B. 2 G 



