104 KOYAL SOCIETY OF CANADA 



Summary of Growth of Colonies in Potash Gelatin. — Colonies ap- 

 peared in 2 days and increased to 1 m.m. in diameter in 4 days. Lique- 

 faction varied with the medium and was delayed by the presence of 

 peptone and especially of peptone and sucrose, though these foods 

 stimulated growth. Peptone was not essential to pigmentation in gelatin 

 with carbohydrates, for in such media, color and pigment grains ap- 

 peared, but the presence of peptone greatly stimulated the production 

 of pigment in such media. 



In peptone gelatin plate cultures without carbohydrates crj^stals 

 formed but no pigment grains; in the same gelatin with carbohydrates 

 pigment grains formed but no crystals. This was also true of test tube 

 cultures. 



Occurrence, position and form of the pigment grains. — These 

 observations apply to the plate cultures which were rich in pigment 

 grains. 



Pigment grains occurred in the colonies, on the colonies and m 

 the gelatin outside the colonies. There were blue-black or sometimes 

 blue, opaque, spherical or rounded, non-crystalline masses from minute 

 size up to 10 // or 18 yu across. Where densely crowded, compound 

 grains might occur but for the most part they were simple. 



Colonies in the same plate differed, having few, many or none of 

 the pigment grains, superficial, internal or external. More of the deep 

 colonies than of the surface colonies had internal pigment grains. Some 

 of the small deep colonies were black and coarsely granular with 

 pigment grains throughout their mass and such colonies were sur- 

 rounded with a zone of these grains in the gelatin beyond their border. 

 Other deep colonies had most of the grains near their centres so that 

 they appeared black centred and, according as these colonies had pigment 

 diffused throughout their mass, or no diffused pigment, they were blue 

 zoned or bro-WTi zoned. Deep colonies and surface colonies had large 

 and less numerous pigment grains distributed evenly in their mass or on 

 their surface. Most surface colonies had the grains not internal but 

 superficial and assembled in several patches which frequently occupied 

 as much as one quarter of the surface. 



Pigment grains were somewhat evenly scattered in the gelatin 

 between colonies if the latter were evenly distributed, but were in a circle 

 around the isolated colonies to the number of 100 or more, and in such 

 zones the size of the grains diminished as the distance from the colony 

 increased. The grains in the gelatin were not equally numerous at 

 all depths but most of them lay in a plane at the depth of the bottom 

 of the surface colonies. 



