234 TEXT-BOOK OF BACTERIOLOGY. 



ture. Eventually, transmitted foreign bacteria will (even when 

 they were originally in the minority or even when there was a 

 single germ of them) cover the tubercle bacilli with their luxuriant 

 growth and irretrievably ruin the culture. 



This danger having been properly obviated, the first commence- 

 ment of colonies becomes visible in about ten to fourteen days after 

 planting. They gradually increase in size and assume a very char- 

 acteristic appearance from the end of the third week. 



We can see with the naked eye the appearance of grayish -white, 

 lustreless, dry, and small crumbs upon the bottom. We notice 

 under the microscope, in the middle, the remainder of the little 

 piece of tissue from which the colony has started. To this are 

 attached variously entwined or simply undulated curved tracings 

 representing the growth of bacteria. Curled in locks and en- 

 tangled, they remind us of strangely-fantastic characters and ara- 

 besques. 



In arranging a " print " preparation of such a colony, we must, 

 of course, stain them in the specific way in order to at once distin- 

 guish the tubercle bacilli as such. It will then be found that the 

 tendril-shaped threads dissolve into a very great number of single 

 rods lying all in about the same direction, close to and behind one 

 another and separated by a distinct and ever-recurring interstice. 

 We frequently perceive here the appearance of those roundish 

 unstained and bright spots in the interior of the rods formerly re- 

 garded as spores. 



As to culture in the test-tube : until recently the exclusive ap- 

 plication of obliquely- coagulated blood-serum had to be resorted to. 

 But since Nocard and Roux have ascertained that our common 

 nutrient becomes, by the addition of 3 to 5$ of glycerin, an ex- 

 cellent nourishing medium for tubercle bacilli, on which they 

 flourish even better than on the serum, the agar thus prepared is 

 preferred and the use of serum has been almost completely dis- 

 pensed with. The latter can only be sterilized with difficulty, for 

 which reason failures of culture resulting from an impure quality of 

 the culture medium have formerly been altogether unavoidable. 

 With the glycerin-agar this danger need not be apprehended, nor 

 can it be doubted that it can be used for the preparation of plates 

 and that it is preferable to serum, although such an experiment 

 has, so far as known, not yet been made. 



If we inoculate the tubercle bacilli with the platinum needle on 

 the surface of the solid, oblique glycerin-agar, the incipient growth 

 will be perceptible, after about fourteen days, throughout the entire 

 extent of the inoculating line. Remaining for one and one-half to 



