344 Journal of Agricultural Research voi. xvi, no. u 



found most common among the orange cocci. One strain has been found 

 which was typical in color upon isolation from soil, but which lost its 

 chromogenesis upon cultivation, not regaining it even after cultivating 

 for a while in sterilized soil. This strain retained its typical morphology 

 and differed from the other cultures at first in no other respect except 

 that it was unable to digest soluble starch. Later it was found to have 

 lost its power of producing nitrite upon nitrate-peptone media. No 

 data are at hand to show whether or not it digested starch before it lost 

 its pigment-producing power. The change in the color of this culture 

 can hardly have been due to an impurity, because three separate sub- 

 strains of this one strain all lost their pigment-producing power at 

 exactly the same time. This shows that chromogenesis, striking as it 

 is in typical cultures, is not an absolutely constant characteristic. 



Physiology. — Perhaps the most striking physiological peculiarity of 

 the organism is the difficulty of cultivating it under laboratory conditions. 

 The only way found to keep it vigorous is by transfers every few days 

 onto agar that has been freshly melted and solidified so as to have con- 

 siderable water of condensation on its surface. This fact is unfortunate, 

 for it makes it practically impossible to keep stock cultures of the organ- 

 ism for purposes of comparison with cultures of other investigators. 



Relation to oxygen. — The organism is very strictly aerobic. In 

 fact, it grows poorly in liquid media, even in an open test tube. 



Liquefaction of gelatin. — All cultures liquefy gelatin. The rapidity 

 of liquefaction varies, although in general it is quite rapid. 



Gelatin colonies usually liquefy to a diameter of about i cm. in four 

 days. Liquefaction is most rapid on the plates made directly from soil, 

 old cultures liquefying more slowly. The colonies have typically a 

 radiate structure, although the typical structure is observed only 

 immediately after isolation from soil. Edges of colonies are entire. 



Ammonia production. — As shown by Bright in the preceding paper, 

 Ps. catulatus is a vigorous ammonifier. 



Action on sugars and glycerin. — In the early work with this organ- 

 ism (Conn, 5, lo) tests for acid production were made in sugar broth as 

 recommended in the report of the committee of water analysis of the 

 American Public Health Association.^ Very irregular results were ob- 

 tained and in mentioning this type (5, p. 103) question marks were placed 

 over those figures in the group number referring to the dextrose, suc- 

 crose, and glycerin, although at that time no evidence at all of acid pro- 

 duction in lactose had been obtained. Later (10, p. 8) it was thought 

 that this irregularity must be due to poor growth in liquid media, so the 

 recent tests have been made in sugar agar containing some indicator. 

 The most satisfactory indicator has proved to be bromcresol purple. 

 Using standard agar in this work, the writer divided the strains studied 



' American Public Health Association. Standards methods for the examination of water and sewage, 

 ed. 2, p, 127-128. New York, 1912. 



