METHODS OF CULTURE AND OF EXAMINATION. 87 



reduced to powder, and introduced into an Erlenmeyer 

 flask with enough distilled water to make a homogeneous 

 soft mass, and sterilized by exposure thrice for an hour each 

 time in the steam-chamber), which is used especially for the 

 cultivation of molds ; also rice-pap (Soyka) (boiled rice-milk 

 sterilized in double glass dishes), which is available for per- 

 manent cultures; infusion of hay y decoction of primes, etc., 

 which may be employed as fluid nutrient media, or in com- 

 bination with gelatin or agar. 



(y) A special position among culture-media is occupied 

 by those free from albuminoids. The constitution of that 

 most frequently employed, and proposed by Uschinsky, is, as 

 modified by Frankel, as follows : 



Potassium biphosphate, 2.0 



Sodium chlorid, 5.0 



Ammonium lactate, 6.0 



Asparagin, 4.0. 



The mixture is dissolved in a liter of water and is ster- 

 ilized. 



METHODS OF CULTURE. 



In nature and in the products of disease individual varie- 

 ties of bacteria are but rarely found isolated that is, alone. 

 Mostly, several species are found together in the material 

 subjected to examination. It is of the utmost importance, 

 in the process of investigation, to separate from one another 

 the different varieties in such a mixture of bacteria that is, 

 to isolate them in pure cidture. This has been rendered 

 possible by the bacteriologic methods introduced by Koch. 

 The principle of these consists in inoculating a solid culture- 

 medium that has been liquefied with a trace of the bacterial 

 mixture to be examined, distributing this as well and as 

 evenly as possible, and then spreading the mixture upon a 

 sterile glass plate. The liquid nutrient medium becomes solid 

 again at room-temperature, and covers the plate in a thin 

 layer, in which the bacteria now develop, but not indiscrim- 

 inately among and next to one another, as in a tube with 

 fluid contents, but separated considerably from one another. 

 At every point where a bacterial germ becomes fixed in the 

 solidifying mass it undergoes isolated development, multi- 

 plying and forming for itself a special colony. By this means 

 it is possible to observe the development and the growth 

 of the individual germs also under the microscope, and to 



