1915] C. H. Crabill and H. S. Reed 35 



cream-constituents is thus prepared. Lipase excreted by the or- 

 ganism splits the butter-fat and the resulting free fatty acids turn 

 the htmus red. In the case of several organisms the Htmus is 

 subsequently reduced to a colorless substance. Ropy-milk bacteria 

 reduce the blue stain without first turning it red, and Diplococcus 

 sp., although it grows fairly well, produces no change in the litmus. 

 See Table 4. 



All but one of the fungi tested cause production of acid from 

 the Cream- fat. Macrosporium, Penicillium and Fusarium show 

 very marked lipolytic activity. Nearly all the bacteria tested are 

 active in breaking up fat. Among the best are B. proteus vulgaris, 

 B. prodigiosus, and B. fliiorescens liqiiifaciens. 



The fat in the cream-agar, prepared as above but without litmus, 

 may be stained with alkannin. The lipolytic action of the bacteria 

 growing on this medium brings about a reduction of the stain. 

 Those organisms which show the strongest acid forming ability on 

 the litmus-cream-agar give also the strongest reactions on alkannin- 

 cream-agar. 



A third series of plates of unstained cream-agar may be em- 

 ployed. The organisms most active on litmus and alkannin in the 

 above tests are also most active in this series. No halo is produced 

 however. Most of the fungi tested digest all of the fat in the agar 

 immediately under the culture and leave it colorless. 



Ethyl butyrate-litmus-agar, prepared as follows, may also be 

 used : To 500 c.c. of the stock agar, 20 c.c. of saturated litmus Solu- 

 tion are added. Enough sodium hydroxid sol. is introduced to 

 give a slight alkaline reaction. Five c.c. of ethyl butyrate are then 

 added, and the medium sterilized and poured into plates. 



B. mycoides, M. citriciis and Oidiuni lactis give a decided red- 

 dening of the agar as a result of acid production by hydrolysis of 

 the ester. Nearly all of the organisms tested grow to some extent 

 on this medium. It is however much less satisfactory than the 

 litmus Cream agar. 



Proteases. The production of proteases is a familiär process, 

 numerous examples of which may be seen daily in the laboratory. 

 The peptonizing action of many organisms, when grown upon 

 gelatin-media, is familiär to all. 



