STREPTOTHRICOSIS. 475 



it may be luxuriant. There is but little tendency for surface growth to spread 

 in any of the cultures, but on the other hand, it heaps up, as it were, giving 

 raised colonies sometimes 1 centimeter above the surface of the media. (See 

 plates.) This is also true with Wright's organism, where surface growth 

 appears. 



Wright first called particular attention to the character of growth in glucose- 

 agar suspension cultures. In this medium with his organism, there is a narrow 

 zone 5 to 10 millimeters below the surface where the colonies are very numerous 

 but small, while lower down they are less numerous, but or larger growth. 

 Surface growth is the rule in our cultures in this medium, and only oecassionally 

 a colony may develop in its depth. 



Stab cultures in sugar-agar. — Growth with Wright's organism occurred in 

 small nodules along the course of the needle, it did not penetrate the medium to 

 any extent and did not grow on or near its surface. 



The growth in our cultures occurs mainly upon the surface and upper portion 

 of the track of the needle. 



Anaerobiosis. — Wright considers his organism as an obligate anaerobe, a 

 statement which is somewhat qualified in the details of his work. For example, 

 in discussing the growth upon glucose-agar suspension media he states that the 

 most profuse growth of the organism is in a narrow zone 5 to 10 millimeters 

 below the surface of the medium and that this way may be "explained as the 

 result of a stimulating action exerted upon the growth of the microorganisms 

 ■ by the presence of a small amount of oxygen which has penetrated into the 

 medium from the surface." This oxygen requirement is further illustrated bj' 

 the author when he states that "in sugar-agar suspension cultures, placed under 

 anaerobic conditions, there is little or no tendency to form colonies on the 

 surface." 



Growth occurred along the course of the needle only in stab cultures on 

 glucose-agar. It did not penetrate the medium and, on the other hand, did 

 not grow on the surface. However, when discussing growth upon surface 

 inoculations in slanted solid media, Wright found that surface growth was not 

 luxuriant and in some of his strains no growth occurred even under anaerobic 

 conditions. Again, Wright observed that "in general, growth appears to be as 

 luxuriant in bouillon either under aerobic or anaerobic conditions." To judge 

 from the above and other statements which might be taken from Wright's 

 excellent monograph and according to the standards used in this report for the 

 other members of the group, Wright's organism must be considered to be a 

 facultative anaerobe. 



In bouillon media there is some variation between the manner of growth of 

 our cultures, but little which may be considered of value in the differentiation 

 of species. The tendency in some of our cultures is toward a surface growth 

 which may gradually separate and fall to the bottom, or settle on the sides 

 of the tube. In other instances, the majority or all of the growth may occur 

 at the bottom of the tube, The medium is not clouded, but in some cases 

 it becomes darker, apparently because of the absorption of pigment from the 

 organisms. There are no essential differences between our cultures in bouillon 

 and those reported by Wright. 



Potato, as is well recognized, is not a very satisfactory medium for compara- 

 tive studies, excepting where the same set of media is used. Fairly luxuriant 

 growth was obtained in every instance with our cultures on potato slants. 2 



- The potato slants employed in this laboratory are made from selected 

 potatoes treated and prepared according to the rules laid down by the committee 

 of the American Public Health Association. 



