96 STUDY OF BACTERIA 



so swiftly that the eye can hardly follow them, or they may merely 

 roll or wiggle across the field slowly. Direct division, if pro- 

 ceeding under the best conditions, requires but fifteen to forty 

 minutes. It is best observed in a warm stage or when working in 

 a room kept at a temperature of 35C. Sporulation occurs differ- 

 ently in different species. In some it will be found soon after the 

 culture has been removed from the incubator, while in others 

 several hours are required. Sporulation, it must be remembered 

 is a resistant stage when unfavorable conditions are met. 



The Gruber-Widal reaction is thus studied. A drop of the 

 serum and bullion culture, mixed in proper proportions, is dropped 

 on a cover-slip, which is then placed, drop downward, over the 

 cavity of the slide (hanging drop, Fig. 20) (see Agglutination) . 



FIG. 20. Hanging drop, over hollow ground slide. (Williams.) 



Staining bacteria is a matter that is easily accomplished, and 

 very many staining solutions and methods have been invented for 

 this purpose. 



The simplest procedure is to take a drop of pus, blood or culture, 

 and spread it upon a very clean slide with a sterilized platinum 

 needle. The matter must be spread thinly and evenly. After the 

 water has evaporated and the preparation has become dry without 

 the use of Jieat, it must be fixed. To do this various agents are 

 used. The object of the fixing is to coagulate the protoplasm of 

 the cells, and to fasten all the smeared matter fast to the glass, 

 so that the staining fluid and water will not wash them off. This 

 is accomplished, for bacteria usually, by holding the smeared slide 

 in the^apex of a bunsen flame until quite warm to the hand. Great 

 care must be used not to char the film. Experience is need( 

 to fix slide smears correctly. The beginner would do well t( 

 use cover-slips. If a cover-slip is used it must be passed througl 

 the flame three times rapidly. After fixing and thorough cooling, 



