556 WILLIAM S. STURGES AND LEO F. RETTGER 



Kolle flasks were empioj'ed in order to supply a maximum 

 surface for growth. The condensation fluid was removed with 

 a pipette and the surface allowed some time to dry, before inocu- 

 lation. The inoculum was taken from j^oung test tube cultures 

 of the same media, and spread over the surface with a bent 

 glass rod. The flasks were incubated for varying lengths of 

 time, usually until the maximum growth was obtained. Bad. 

 coli and the different cocci were grown at 37°C. The other 

 cultures were incubated at 24 to 30°. The harvesting was 

 accomplished by scraping the growth from the surface with a 

 stiff steel Tvire and transferring to sterile glass-stoppered bottles. 

 Suspensions were then made by adding sterile O.S per cent sodium 

 chloride solution, or in some instances distilled water, and shaking 

 vigorously. After filtration through sterile cotton two to five 

 per cent of toluol was added and the bottle well shaken. After 

 the withdrawal of a small portion of the suspension for preliminary 

 examination, the bottles were placed in the incubator. They were 

 shaken frequently and samples withdrawn from time to time 

 for analysis. The different analyses were made as follows: 



The biuret test 



Twenty cubic centimeters of 4 per cent NaOH were measured 

 into a Nessler tube and 2 cc. of f^ normal CUSO4 added. A 

 measured amount (usually 0.1 to 0.5 cc.) of the supension was 

 introduced with a sterile pipette. The amount was gauged 

 by the intensity of color that developed. The most accurate 

 readings are made if the test is so regulated as to give a com- 

 paratively faint color. Color comparisons were made with 

 standard tubes to wliich definite but varying amounts of Witte's 

 peptone had been added. The color strength was expressed 

 in the terms of the percentage of "Witte's peptone to which the 

 unknown was equal in biuret-giving properties. It was found 

 advantageous to use 0.1 per cent "Witte peptone solution which 

 (within the range of 0.1 to 2 cc.) in the standard tubes gave 

 readable differences in 0.1 cc. gradations. These represent 

 gradations of 0.1 mgm. of Witte's peptone. One cubic centimeter 

 is a fair amount of the unknown to use for a test. One tenth 



