CULTIVATION BY STROKE AND PUNCTURE. 63 



A very cotnmoQ mistake with beginners is to trans- 

 fer too large a quantity of the colony to the naedium. 

 Only so small an amount should be allowed to remain 

 on the platinum wire as is just perceptible to the 

 naked eye. If too much of the old cultivation is 

 introduced into the new, numerous cells which are 

 scarcely living, and which are very dififerent in appear- 

 ance from the typical one, are sure to be introduced 

 into the medium, and these may cause much confusion 

 in the preparation, and often make the culture appear 

 to be impure. 



In these stroke cultures many peculiarities now 

 come into prominence, which were scarcely percept- 

 ible in the plate cultivations. The colonies may 

 confine themselves to the actual inoculating stroke, or 

 they may spread themselves out, to a greater or less 

 degree, until the whole surface of the nutrient medium 

 is covered right up to the sides of the test-tube. 

 They may flourish only on the surface, as is generally 

 the case, or they may send down hair-like or radiating 

 runners into the interior. In some cases peculiar 

 skin-like ridges may be formed, and whilst some 

 colonies shine brightly, others only do so faintly, and 

 yet others do not shine at all ; others remain as iso- 

 lated drops which do not coalesce, and so on; in 

 short, we find a series of specific characteristics, which 

 either do not show themselves in plate cultures or are 

 so insignificant as to escape observation. 



