STAB CULTURES 149 



Subcultures, or Transplants. After bacteria have been obtained in 

 pure cultures by one of the methods described, it is always necessary 

 to prepare, from time to time, fresh cultures, because numerous micro- 

 organisms soon show a tendency to die out in an artificial culture 

 medium, on account of the accumulation of their own metabolic 

 products or for other reasons. The transfer of an older culture to a 

 new, fresh, sterile culture medium is made in such a manner that 

 the danger of air and other contaminations is reduced to a minimum. 

 This is accomplished by flaming the cotton and upper ends of the 

 tubes or flasks containing the growth, as well as those of the new 

 ones to be inoculated; or, when Petri dishes are used, by only lifting 

 the lid sufficiently to allow the introduction of the platinum loop. 

 The procedure of inoculating new tubes or flasks from preexisting 

 pure cultures is called making a subculture, or transplant (trans- 

 planting the cultures). 



The first pure culture obtained from pathologic or other material 

 is spoken of as the first generation; the first transplant as the second, 

 the next transplant as the third generation, and so forth. A culture 

 tube should always be so labelled that it clearly shows the kind of 

 culture medium, the kind of microorganism, its derivation, the gener- 

 ation, the date w T hen the original inoculation, or transplant, was made, 

 and something about the manner in which it has been raised. A 

 sufficiently designated culture would, for example, show the following 

 inscription on the label 



Glycerin Agar 

 Bacillus Anthracis 

 Blood of mouse dead from Anthrax 

 Fourth Generation 

 January 15, 1910 

 (Incubator, kept aerobically) 



It is, of course, not necessary to label as elaborately the cultures used 

 by students for laboratory exercises, but the culture medium, the 

 species of bacterium, and the date of inoculation must always be given, 

 and they should be repeated on the label of the microscopic prepar- 

 ation. It is also desirable to indicate on the latter the stain used. 



Streak Cultures. The described method of making an original 

 culture or a transplant by drawing the platinum loop over the slanting 

 surface of agar or over a potato half-cylinder in a test-tube is called 

 a streak culture. There is no special name for the inoculation of the 

 fluid media. 



Stab Cultures. Gelatin of any kind and sugar agar are generally 

 not prepared in test-tubes in a slanting position, but as a solid cylinder 

 at the bottom of the tube. This condition is brought about by keeping 

 the tubes in an upright position at the time when the media solidify. 

 Such media are inoculated with the platinum wire straightened out 

 into a needle. The outer free end of the wire, after sterilization 

 over a flame and subsequent cooling, is brought in contact with the 



