LEO F. RETTGER 649 



numbers and activities of certain types of intestinal organisms, namely, the aciduric 

 {L. acidophilus and L. bijidus). Representative portions of feces (large, well-rounded 

 loopfuls) were vigorously shaken in rubber-stoppered, thick-walled test tubes con- 

 taining ID cc. of physiological saline solution and broken glass. The suspensions were 

 then diluted to a turbidity of about 8.0 on the McFarland nephelometer scale. These 

 constituted the stock suspensions. For the determination of colonies of the aciduric 

 organisms (particularly L. acidophilus) special agar medium is employed. This may 

 be either whey' or casein digest^ agar, or, as has been shown quite recently, a special 

 tomato-peptone agar. The agar plates are incubated in closed containers in an atmos- 

 phere containing 5-10 per cent carbon dioxide.^ For the estimation of colonies of organ- 

 isms not aciduric, ordinary agar plates are used. For a comparative study of gas pro- 

 duction the Veillon tube as described by Veillon and Zuber-* is used, with the following 

 modification. Instead of having one end of the g-inch tubing permanently sealed, it is 

 left open for the insertion of a rubber stopper. The other end is plugged with cotton. 

 Direct microscopic examination is made of slide films prepared from the stock emul- 

 sion and stained by the gram method. The preliminary coating of the slides with a 

 very thin layer of dilute egg albumin enables the films to adhere more permanently to 

 the slides. 



Special objects require modification of methods and media. For example, in 

 studying the fate of bakers' yeast in the intestine, the agar medium of Reddish^ may 

 be employed. This consists of malt extract (powdered) 100 gm., agar 15 gm,, and 

 water 900 cc, and has a H-ion concentration of pH 5.5-5.6. 



' Rettger, L. F., and Cheplin, H. A.: Intestinal Flora. New Haven: Yale University Press, 1921. 



' Kulp, W. L.: Bad. Abstr., 7, 9. 1923. 



' Kulp, W. L.: Science, 64, 304. 1926. 



^Veillon and Zuber: A)-ch. dc med., 10, 517. 1898. 



5 Reddish, G. F.: Abstr. Bad., i, 6. 1919. 



