Esmarch's Tubes 207 



flame, instead of in the hot-air closet, special forceps adapted to 

 holding them having been devised by Rosenberger. * 



The dilution of the material under examination is made with gela- 

 tin or agar-agar tubes in the manner above described, the plug is 

 removed, the mouth of the tube cautiously held for a moment in the 

 flame, and the contents poured into one of the sterile dishes, whose 

 lid is just sufficiently elevated to permit the mouth of the tube to 

 enter. The gelatin is spread over the bottom of the dish in an even 

 layer, allowed to solidify, labeled, inverted, so that the water of con- 

 densation may not drop from the lid upon the culture film and spoil 

 the cultures, and stood away for the colonies to develop. 



Fig. 55- Esmarch tube on block of ice (redrawn after Abbott). 



To overcome the difficulty of excessive water of condensation Hill 

 has introduced lids made of porous clay, by which the moisture is 

 absorbed. These can be obtained from most laboratory purveyors. 



Among the other advantages of the Petri dish is the convenience 

 with which colonies can be studied with a low-power lens. To do 

 this with the Koch plates meant to remove them from the sterile 

 chamber to the stage of a microscope and so expose them to the air, 

 and to contamination, but to examine colonies in the Petri dish, one 

 simply examines through the thin glass of the bottom dish without 

 any exposure to contaminating organisms. 



Esmarch's Tubes. This method, devised by Esmarch, converts the wall of 

 the test-tube into the plate and dispenses with all other apparatus. The tubes, 

 which are inoculated and in which the dilutions are made, should contain less 

 than half the usual amount of gelatin or agar-agar. After inoculation the cotton 

 plugs are pushed into the tubes until even with their mouths, and then covered 

 with a rubber cap, which protects them from wetting. A groove is next cut in a 

 block of ice, and the tube, held almost horizontally, is rolled in this until the entire 

 surface of the glass is covered with a thin layer of the soldified medium. Thus 

 the wall of the tube becomes the plate upon which the colonies develop. 



In carrying out Esmarch's method, the tube must not contain too much of 

 the culture medium, or it cannot be rolled into an even layer; the contents should 

 not touch the cotton plug, lest it be glued to the glass and its subsequent useful- 

 ness injured, and no water must be admitted from the melted ice. 



* "Phila. Med. Jour.," Oct. 20, 1900, vol. vi, No. 16, p. 760. 



