28 



Papers from the Marine Biological Laboratory at Tortugas. 



the jelly set in irregular waves and lumps. Consequently the samples were 

 kept on ice, and cultures were made from them at Plymouth 24 hours after 

 collection. It is clear that in future attempts to make plate cultures on 

 board a small boat in rough weather, a very delicately swung table will be 

 necessary, or else the roll-tube culture method must be employed. 



Three plates on peptone agar were made from each sample, i c.c. of 

 the sample being used for each plate. The plates were kept at the room 

 temperature, averaging about 20** C, and the colonies were well developed 

 after 48 hours; they appeared to be all of one kind. A count gave the 

 following results : 



The increase in the number of colonies at 70 and 80 fathoms is somewhat 

 remarkable, but no conclusions in this respect can be drawn from one series 

 of observations. 



The cultural characteristics of this bacterium are as follows : 



On peptone agar, after about 36 hours at 20° C, the colonies are white 

 in color, circular, with a finely serrated outline and a coarsely granular 

 appearance. Superficial colonies grow very rapidly, and may spread as a 

 whitish semi-transparent growth of irregular shape over the surface of the 

 agar. The deep colonies remain small, globular, and discrete. In old agar 

 cultures a brownish tinge is developed, and the color may diffuse through 

 the substance of the agar. On gelatin peptone growth was rapid; in stab 

 cultures growth proceeded from the surface downwards, leaving a funnel- 

 shaped depression of liquefied gelatin, and eventually all the gelatin became 

 liquefied. 



Acid formation, as shown by the neutral-red reaction, took place in 

 dextrose, mannite, and Isevulose, but not in cane sugar or lactose media. 



One thousand c.c. of Gran's medium, inoculated on board with 10 c.c. 

 of a surface sample immediately after collection, and kept at an average 

 temperature of about 20° C, showed the first trace of nitrite formation 

 after 70 hours. After 84 hours a very strong nitrite reaction was obtained, 

 and a slight ammonia reaction was given with Nessler's reagent. The proc- 

 ess of denitrification, even after the lapse of weeks, did not extend beyond 

 this, and no bubbles of gas were formed. Other experiments made with 

 subcultures from agar and gelatin media gave similar results, so that it 

 appears that this bacterium can not entirely break down nitrates at a 

 temperature of 20° C. The optimum temperature for denitrification pro- 

 duced by this bacterium appears to be about 20° C, as the process was less 



