132 BIOLOGY AND TECHNIQUE 



any time. It is also possible, though less regularly yielding good results, 

 to sterilize in the inspissator for one day, following this on the second 

 and third days by exposure for thirty minutes to 100° C. in the Arnold 

 steam sterilizer. In doing this, the Arnold should be very gradually 

 heated, at first without outer jacket, this being lowered only after 

 thorough heating has taken place. 



Serum-Water Media for Fermentation Tests. — For the deter- 

 mination of the fermentative powers of various microorganisms 

 for purposes of differentiation, Hiss has devised the following media 

 in which the cleavage of any given carbohydrate is indicated, 

 not only by the production of an acid reaction, but by the coagulation 

 of the serum proteids. 



Obtain clear beef serum by pipetting from clotted blood in the same 

 way as this is obtained for the preparation of LoefHer's blood-serum 

 medium. Add to this two or three times its bulk of distilled water, 

 making a mixture of serum and water in proportions of one to two or 

 three. Heat the mixture for fifteen minutes in an Arnold sterilizer at 

 100° C. to destroy any diastatic ferments present in the serum. Add 

 one per cent of a five per cent aqueous litmus solution (the varia- 

 tion in the different litmus preparations as obtained in laboratories 

 necessitates a careful addition of an aqueous litmus solution until 

 the proper color, a deep transparent blue, is obtained, rather than 

 rigid adherence to any quantitative directions). Add to the various 

 fractions of the medium thus made one per cent respectively of the 

 sugars which are to be used for the tests. 



For the preparation of inulin medium, made in this way for pneu- 

 mococcus-streptococcus differentiation, it is necessary to sterilize the 

 inulin dissolved in the water to be added to the senmi in an autoclave 

 at high temperature (15 pounds for 15 minutes) in order to kill spores 

 before mixing with the serum. The serum-water media are sterilized by 

 the fractional method at 100° C, at which temperature they remain fluid. 



Special Media for Colon-Typhoid Differentiation.' — Hiss' Plating 

 Medium.^ — The composition of this medium is as follows: 



Agar 15 gms. 



Gelatin 15 " 



Liebig's meat extract 5 " 



Sodium chloride 5 " 



Dextrose 10 " 



Distilled water 1,000 c.c. 



1 For details of use of these special media see also chapter on BaciUus tj^phosus. 

 ^Hiss, Jour. Exp. Med., ii, 1897; Jour. Med. Research, viii, 1902. 



