38 



^K 



m 



ZOOGLCEJE. 



Zoogloese are usually" developed in solid and fluid cultures after a 

 few days, the time of appearance varying greatly with the nature of 

 the medium. In general they appeared much sooner in acid fluids 



than in alkaline ones. In beef broth made very 

 ^1 stronglj' alkaline to litmus (neutral to phenolphta- 

 lein) by means of caustic soda, they did not appear 

 until the close of the second week. In acid beef 

 broth (unneutralized) they were commonly visible 

 to the naked eye a daj' or two after clouding. In 

 one instance, however, they appeared in an alkaline 

 gelatin culture the second day after inoculation and 

 were very numerous the third dsLj. This gelatin 

 was strongly alkaline with caustic soda (neutral to 

 phenolphtalein) and was in a fluid state (28° to 29° 

 C), i. e., in a condition where any substance unfa- 

 vorable to growth could act on the organism most 

 effectively. May it not be that the zoogloea stage is 

 a f>rotective state entered into by bacteria whenever 

 the physical or chemical conditions of the substra- 

 tum are unfavorable to growth, these conditions 

 being either independent of the organism, as in this 

 case, or brought about by its own metabolism? 



In beef In-oth and other fluid cultures the tiny 

 aggregations of this organism showed a marked 

 tendencj^ to gather into a ring or rim on the wall of 

 the tube at the level of the liquid, and sometimes 

 floating islands appeared, but the flocculent matter 

 seldom united into any tough pellicle, being easily 

 jarred apart and into the depths of the fluid. These zooglo^fe appear 

 to the naked eye either as small whitish flecks or, Avhen on the rim at 

 the surface of the liquid, as round, yellow, colony-like bodies, espe- 

 cially when they have reached some age and 

 density. These bodies also formed on substrata 

 rich in assimilable sugars; here, perhaps, owing 

 to the development of acids. On the solid, sugar- 

 rich substrata, e. g., sugar-agar, potato with 

 sugar, sugar beet, sweet potato, etc., they pro- 

 duced a papillose, verrucose, or shagreen-like 

 surface, the tiny rounded elements forming this 

 surface being very smooth and distinct in their 

 upper part, but fused below next to the substratum. This shagreen 

 also appeared, on old cultures, on nutrient starch jelly containing 5 per 

 cent glycerol. This appearance is shown in figs. 3 and 4. 



Flu. o.— Culture of 

 Pseudomonas hya- 

 cinthi on slant 30 per 

 cent cane-sugar agar, 

 showing "shagreen" 

 surface. 



Fig. 4.— Slightly magnified 

 diagrammatic views of 

 slime of Ps. hyacinthi on 

 sweet potato, showing 

 "shagreen ■■ surfaoe. 



