410 F. M. Rolfs 



of the organism which had been exposed for one-half minute and for five 

 minutes. No colonies appeared on any of the plates on which the or- 

 ganism had been exposed for fifteen minutes and for thirty minutes. 



In arsenate of lead, 1-208 dilution, colonies appeared on all plates on 

 which the organism had been exposed for one-half, five, fifteen, and thirty 

 minutes, respectively. 



Diastatic action. — The test for diastatic action was made on potato 

 cylinders. Twenty-eight strains of the organism were grown on potato 

 cylinders for twenty-five days. The cultures were then tested for starch 

 reduction, and only one of the strains showed marked diastatic action. 

 In all the other cases the only indications observed were a slow and slight 

 tendency toward the conversion of starch into amylodextrin, shown by a 

 gradual change in the iodine reaction from a clear blue to a purplish tint. 



These tests were made according to the directions given by Harding 

 and Morse (1909): " These potato cultures were crushed in porcelain 

 mortars and 50 cubic centimeters of water added to separate the particles 

 so that the effect of the iodine could be easily seen. The presence of 

 unchanged starch was determined by the gradual addition of a weak 

 solution of iodine in potassium iodide. After a sufficient amount has been 

 added to satisfy some of the other compounds which are present the starch 

 grains are turned to a blue-black. The extent of the reduction of the 

 starch by the bacterial growth is estimated on the basis of similar tests 

 of uninoculated potato cylinders." 



The uninoculated cylinders, when tested with the iodine-potassium- 

 iodide solution diluted with water, always yielded a bright blue reaction. 

 The starch reaction was also strong after the organism had been grown 

 on the cylinders for several weeks, although a purplish color indicated a 

 slight diastatic action. 



Fragments of potato scraped from under the yellow slime from a culture 

 forty days old, mixed with about twenty times their bulk of water, gave 

 a purple or a blue-purple reaction. When fragments of material from the 

 back or the center of the cylinder were used and treated in the same way, 

 they invariably gave the blue reaction. The water below the potato 

 cylinder, when it contained more or less of the yellow slime of the organ- 

 ism, also invariably gave a purplish blue reaction. 



Pepsin. — A peptonizing ferment must be present, since gelatin is 

 liquefied and casein is slowly dissolved with the formation of tyrosine. 



