178 BIOLOGY AND TECHNIQUE 



Separation of Bacteria by Surface Streaking. When it is neces- 

 sary to isolate bacteria like the gonococcus Bacillus influenzas, the 

 pneumococcus, and others, which, because of great sensitiveness to 

 environment and possibly a preference for free oxygen, are not 

 readily grown in pour plates, it is often advantageous first to pour 

 plates of suitable media, allow them to harden, and then gently 

 smear over their surfaces dilutions of the infectious material, usually 

 in three or four parallel streaks. 



Upon such plates, if dilutions have been properly made, and 

 this is only a question of judgment based upon an estimation of the 

 numbers of bacteria in the original material, discrete colonies of 

 the microorganisms sought for may develop, and can be " fished" 

 in -the usual manner. 



The media most favorable for the cultivation of various micro- 

 organisms will be discussed in the sections dealing with the in- 

 dividual species. 



BARBER PIPETTE METHOD FOR THE ISOLATION OF SINGLE MICRO- 

 ORGANISMS. Although we consider this one of the very important 

 methods of bacteriological study, we shall give no extensive descrip- 

 tion of" the apparatus or the manner of using it, because both are 

 too complicated to permit of satisfactory use from text book descrip- 

 tion. The principle of the method depends upon a specially pre- 

 pared mechanical stage adjusted to a compound microscope on which 

 there is a moist chamber closed with a large coverglass, on the 

 bottom of which drops of fluid, containing bacteria can be placed. 

 A very fine glass pipette, manipulated by a specially constructed 

 pipette holder and with a rubber tubing attached, is governed by 

 observation through the microscope and by means of it small drops 

 of the fluid are taken up, an attempt being made to obtain a single 

 microorganism in these drops. With a little practice this can be 

 accomplished, and these separate drops in which the individual 

 bacteria can be seen swimming about, are made to suspend from 

 the bottom of the cover, slip, closing the top of the moist chamber. 

 The apparatus can be understood and worked only by practice and 

 suitable instruction, together with a study of the description given 

 by Barber in his article in the Philippine Journal of Science. 2 The 

 apparatus is made by a number of firms under the name of the 



2 Barber, Philippine Jour, of Science, Sec. B, Vol. 9, No. 4, August, 1914. 





