1S8 SPECIAL BACTERIOLOGY 



on to the surface of bjood serum medium. The whole process must be 

 accomplished quickly and with the greatest cleanliness, because if 

 another germ enters the serum tube, it will soon outgrow the tubercle 

 bacillus. As a greater precaution, several cultivations ought to be 

 instituted at the same time. The cultures remaining a long time 

 in the incubator at 37 to 38 C., they must be closed with indiarubber 

 caps previously sterilized in sublimate solution, or the superfluous over- 

 hanging cotton -plug burnt off in the flame, and the tube closed with 

 melted paraffin or sealing-wax. Without these precautions the water of 

 condensation will be all absorbed arid the culture medium dried up. 



When the inoculation is successful, signs of growth are observed in 

 fourteen days in the blood serum tubes. Small, grey, dry scales develop, 

 which when examined under a low power appear composed of delicate 

 twisted lines. The development goes on slowly, and in four to six 

 weeks other tubes can be inoculated from the original culture. The 

 growth of the second generation requires two weeks before it is distinct. 

 Later generations, usually the fifth or sixth, grow more luxuriantly and 

 quicker, especially when a special incubator is used, provided with an 

 atmosphere of steam, so that the use of indiarubber caps, etc., can be 

 dispensed with. Under such conditions, in seven to fourteen days the 

 whole of the surface of the serum medium is covered with the character- 

 istic dry scales. From the fifth serum generation it is easy to obtain 

 cultures on glycerine agar. On this medium the development is much 

 more abundant, the bacilli forming a greyish dry coating of brittle, 

 curly, slightly elevated fragments (see Photograph, Fig. 48). 



This coating growing downwards, covers any water of condensa- 

 tion present without clouding it, and when the culture is left long 

 enough in the incubator it grows a considerable distance up the free 

 sides of the test-tubes, where no nutrient medium is present. Veal 

 bouillon, with 6 per cent, glycerine added, and filled in Erlenmeyer 

 flasks, is the best fluid medium. When inoculating this bouillon it is 

 necessary to place the dry scales in the fluid so that they swim on the 

 surface, as the tubercle bacilli, being susceptible to oxygen, develop only 

 in the upper portions of the medium where the air has sufficient access. 

 On the surface of veal 6 per cent, glycerine bouillon the tubercle bacilli 

 form a membranous surface growth which exhibits the same char- 

 acteristics as the coating on glycerine agar. Under favourable 

 circumstances, in a few weeks, sometimes in ten days, the growth extends 

 a considerable distance up the walls of the tube ; the lower portion of 

 the bouillon remains perfectly clear, which is a characteristic of the growth 

 of the tubercle bacillus. 



On Potatoes) the under ends of which project into a solution contain- 

 ing 5 per cent, of glycerine and 5 per cent, of NaCl., placed in the 

 bottom of the tube, the tubercle bacilli develop very well, forming on 

 the surface of the potatoes thick warty tufts, the glycerine solution 



