TUBERCULOSIS. 379 



blood serum. Solid blood serum, with or without the addition of 

 gelatine, was employed, and the cultures incubated at 37° C. The 

 growth takes place very slowly, and only between the temperatures 

 of 30° 0. and 41° C. In about eight or ten days the growth appears 

 as little whitish or yellowish scales and grains. 



The bacillus can also be cultivated in a glass capsule, on blood 

 serum, and the appearances of the growth studied under the 

 microscope. The scales or pellicles were described by Koch as made 

 up of colonies of a perfectly characteristic appearance, which may 

 be still further studied by making a cover-glass impression. They 

 are then seen to be composed of bacilli, arranged more or less 

 with their long axis corresponding with that of the colony itself, 

 and with an appreciable interval between the individual bacilli. 

 The colonies themselves appear as fine curved lines, the smallest 

 being mostly S "Shaped. Longer colonies have serpentine twistings 

 and bendings, which often 

 recall the curves of fancy 

 lettering. The ends of the 

 lines run to sharp points, 

 but the middle of the 

 growth is spindle-formed. 

 The youngest colonies are 

 extremely delicate and 

 narrow, but the older 

 colonies increase in size, 



are thicker across, and, i""'^- 164. -Bacillus TUBBEonLOSis, fkom 

 , TuBEEOULAB SpcTUM, X 2500. From Photo- 



blending with each other, graphs. 



gradually obliterate the 



characteristic appearances; a lamellated growth results, which 

 increases, and gives the appearance to the naked eye of the scale 

 or pellicle already described. The blood serum is not liquefied 

 unless putrefactive bacteria contaminate the culture. A fresh tube 

 can be inoculated with one of the little scales, and a new generation 

 started. The scales gradually increase in size, and consist entirely 

 of bacilli. In about three to four weeks the cultivation ceases to 

 increase, and it is then necessary to inoculate a fresh tube. 



In liquid blood serum a film forms on the surface of the liquid, 

 and is easily broken by agitation. In neutralised broth there is 

 very little indication of success. When a triturated culture is added 

 to the broth, a granular, sandy, whitish deposit collects at the 

 bottom of the vessel, with indications of an increase in amount. 

 Koch also tried nutrient agar-agar, which did not prove to be at 



