BACTERIOLOGICAL TECHNIC 



83 



with the tip of a heat-sterilized (by holding in flame of Bunsen burner until 

 red hot) platinum needle (prepared by fusing a platinum wire, i3^ Inches 

 long, into the end of a glass rod, six to seven inches long), then removing 

 the cotton plug from the test-tube, and pushing the needle, carrying the 

 microbes, into the culture medium down to the very bottom of the tube. 

 Replace the cotton plug at once, pass the needle into the flame of the Bunsen 

 burner until red hot, to sterilize it, and lay aside for the next tube inocu- 

 lation. This is known as a deep stab tube inoculation. In this manner 

 inoculate some five or six tubes. Also make streak 

 inoculation on tube slants by simply passing the in- 

 fected platinum needle over the middle of the tube 

 slant surface, from lower end toward the top, ob- 

 serving the instructions regarding the cotton plug 

 and needle sterilization, with each tube inoculation. 

 Number the tubes serially, and in a special note- 

 book make entry of all desirable data pertaining 

 to each inoculation, making such entries under 

 each tube number. Place tubes vertically in a 

 suitable holder, as tumbler, beaker, wire basket, 

 etc., and set aside in incubator or in some container 

 to which you alone have access. 



In warm weather the first bacterial growths may 

 appear at the end of thirty-six hours. In cold or 

 cool weather nothing may appear for two, three, 

 and even four to five days. Note the nature of the 

 bacterial growth in a deep stab inoculation and in 

 the streak inoculation, as to 



a. Growth — scanty, moderate, abundant; slow, 

 rapid. 



b. Form of growth — outUne clearly defined, 

 spreading, rugose, beaded, etc. 



c. As to surface — flat, raised, concave, convex. 



d. Color — translucent, ghstening, waxy, trans- 

 parent, opaque, fight, chalky white, grayish- white, 

 dark red, green, blue, yellow, lemon color, purple, 



etc. 



e. Odor — comparative description. 



f . Consistency— wiscid, slimy, stringy, membranous, friable or brittle, 



dry, watery, etc. 



g. Changes in medium— gela.tin liquefied, gelatin not fiquefied; 

 colored, as grayed, browned, reddened, blued, etc. In case indicators 

 are used, any color changes should be noted. 



Fig. 33. — Kitasato 

 filter for filtering hypo- 

 dermicsolutions, culture 

 media, sera, water, etc. 

 The material to be filt- 

 ered is placed in the 

 globose container and 

 forced through the clay 

 (infusorial earth) tube 

 (Berkefeld filter bougie) 

 by connecting the re- 

 ceiver with a vacuum, 

 pump. All parts of the 

 filter must, of course, be 

 sterilized by heat be- 

 fore and after using. 

 {Williams.) 



