TEST-TUBE CULTIVATIONS. 69 



expected that such a brilliant transparency can be 

 obtained as with gelatine. The final result, when 

 solid, should be colourless and clear, but if only 

 slightly milky it may still be employed. 



After the final treatment in the steam steriliser 

 some of the tubes may be placed in the blood- 

 serum apparatus, and left to gelatinise with an 

 oblique surface. A little liquid gradually collects 

 at the bottom of the surface, being expressed by the 

 contraction of the nutrient jelly. 



(B) METHODS OF EMPLOYING NUTRIENT JELLY IN 

 TEST-TUBE- AND PLATE-CULTIVATIONS. 



Test-Tube-Cultivations.- To inoculate test- 

 tubes containing nutrient jelly, the cotton wool plug 

 must be twisted out, by which means any adhesions 

 that may exist are broken down. A sterilised 

 needle charged with the blood, pus, etc., containing 

 the micro-organisms, or with a colony from a 

 plate-culture, is steadily thrust once, and once 

 only, into the nutrient jelly. The tube should be 

 held with its mouth downwards, to avoid, as far 

 as possible, accidental contamination from the 

 gravitation of germs in the air, and the plug, 

 which has been removed with the thumb and index 

 finger of the right hand and held between the 

 fourth and fifth fingers of the left, is replaced 

 as rapidly as possible (Fig. 27). 



The chances of error arising from contamination 



