22 BACTERIA 



^" ^gg' Glycerine and grape-sugar may be added as else- 

 where. Blood agar is ordinary agar with fresh sterile blood 

 smeared over its surface. Blood sertiin is drawn from a jar 

 of coagulated horse-blood, in which the serum has risen to 

 the top. This is collected in sterihsed tubes and 

 coagulated in a special apparatus (the serum in- 

 spissator). Potato is prepared by scraping ordin- 

 ary potatoes, washing in corrosive sublimate, and 

 sterilising. They may then be cut into various 

 shapes convenient for cultivation. Upon any of 

 M these forms of solid media the characteristic 

 U growth of the organism can be observed. Of the 

 Potato in a nutrient elements required, nitrogen is obtained 



ROUXTUBE . 



Prepared for from albumeus and proteids, carbon from milk- 

 CuLTivATioN gyg^j.^ cane-sugar, or the splitting up of proteids ; 

 placed in the salts (particularly phosphates and salts of potas- 

 buibof thetubegium) are readily obtainable from those incorpor- 

 ated in the media ; and the water which is required is 

 obtainable from the moisture of the media. 



There are two common forms of test-tube culture, viz. : on 

 the surface and in the depth of the medium. In the former 

 the medium is sloped, and the inoculating needle is drawn 

 along its surface ; in the latter the needle is thrust vertically 

 downwards into the depth of the solid medium. Plate cul- 

 tures and anaerobic cultures will be described at a later 

 stage. When the medium has been inoculated the culture 

 is placed at a temperature which will be favourable. Two 

 standards of temperature are in use in bacteriological labora- 

 tories. The one is called rooin temperature, and varies from 

 i8° C.-20° C. ; the other is blood-heat, and varies from 35° 

 €.-38° C. It is true, some species will grow below 18° C, 

 and others above 38° C. The pathogenic (disease-producing) 

 bacteria thrive best at 37° C, and the non-pathogenic at the 

 ordinary temperature of the room. The different degrees 

 of temperature are regulated by means of incubators. For 



