Another method which is frequently applicable with material from human or animal sources is to (3) _rub the material over the surface_ of a slope tube or of medium solidified in a Petri dish with a sterile heavy platinum needle, glass rod, or cotton swab. If the bacteria are not too numerous, pure cultures may frequently be obtained. A modification of this method is to make a series of (4) _parallel streaks on a slope tube or plate of medium_ with a needle inserted _but once_ into the material to be plated. On the first streak most of the bacteria are rubbed off and a continuous growth results, but usually on the last of a series only isolated colonies appear, which are presumably pure. The ideal method for securing pure cultures is to be absolutely certain that the culture starts from a single organism. This may be accomplished by means of the (5) _apparatus and pipettes devised by Professor Barber_ of the University of Kansas (Figs. 135 and 136). With this instrument a single organism is picked out under the microscope and isolated in a drop of culture medium and observed until it is seen to divide, thus proving its viability. Transfers are then made to the proper media. The method requires much practice to develop the necessary skill in the making of pipettes, determining the proper condition of the large cover-glasses used over the isolating box, and in manipulation, but the results fully compensate. [Illustration: FIG. 133.--From the thinnest part of plate _2_, Fig. 131 as seen under the low-power objective. × 100. Colonies much larger than on plate _1_, but still crowded.] [Illustration: FIG. 134.--The smallest colony on plate _3_, Fig. 131, as seen under the low-power objective. × 100. Large, single, isolated colony.] Professor W. A. Starin of the author’s department, a former student of Professor Barber, has done some excellent work with this apparatus. [Illustration: FIG. 135.--Diagram of Barber’s isolation apparatus. _b_, moist chamber; _ms_, large cover-glass over moist chamber; _p_, small pipette drawn out to a fine point; _k_, _r_, _g_, pipette holder; _f_, screw for raising and lowering _k_, _r_, _g_; _s_, screw for lateral motion of _k_, _r_, _g_; _n_, screw for clamp on pipette which allows it to be moved in or out; _m_, mechanical stage of microscope; _t_, rubber tube held in the mouth and used to move the liquid culture medium in the pipette. (Journal of Infectious Diseases, October 20, 1908, vol. 5, No. 4, p. 381.)] [Illustration: FIG. 136.--Photograph of microscope with Barber’s isolation apparatus set up to use.]