20 BACTERIA IN RELATION TO PLANT DISEASES. 



cially commended by Dr. Welch ('92, Bibliog., XIII), the capsule is also stained, but 

 remains distinctly paler than the body of the bacterium. They may also be counter- 

 stained, as in Muir's method or Moore's method. Well-defined capsules are shown 

 in fig. iia. This may be compared with fig. 12, in which the same organism is 

 shown without capsules. Fig. iid shows the extreme viscidity of a culture due to 

 the formation and deliquescence of capsules. Fig. 13 shows the tenuous threads 

 into which Bacillus tracheiphiliis may be drawn as it oozes from the cirt steins of 

 cucurbits. Fig. 14 is a detail from the same more highly magnified, the viscid con- 

 necting substance being irnstained. 



FLAGELLA. 



Ehrenberg was the first to describe flagella on bacteria {Bacterium triloculare^ 

 1838). Nothing more was done until 1872, when Cohn discovered them on Spi- 

 rillum volutans. In 1875 Dallinger & Di'^'sdale saw and figured them on Bacterium 

 tcrmo. In 1875 Warming determined their existence on J^ibrio rugula and Spi- 

 rilluui undula. In 1877 Koch demonstrated their existence on a number of species 

 by the use of stains. In 1878 Dallinger, using unstained material, saw them many 

 times on Bacterium tcrmo and also on Spirillum volutans. After 1879 no one 

 appears to have disputed their existence. In 1890 Messea proposed to divide the 

 fliagellate bacteria into four large groups, monotrichiate, lophotrichiate, amphitri- 

 chiate, and peritrichiate. In 1895 Fischer used the flagella as marks to distinguish 

 subfamilies. In the previous year Migula used their number and mode of attachment 

 as a means of distinguishing genera. 



The staining of flagella has now become a regular part of laboratory work. 

 Their number aud position on the body wall should be determined, if possible, in 

 case of each species studied. This is sometimes quite easy and at other times vers' 

 difficult. It should also be determined whether the flagella are fugitive or persistent. 



Flagella may be stained from young agar cultures. Bouillon cultures are to be 

 avoided because of the intense ground stain. Some kinds may be stained readih- 

 from cultures grown for some days in a very dilute Uschinsky's solution — i to 3 

 drops in 10 cc. of distilled water (fig. 15). The flagella of some bacteria are stained 

 readily, those of others only with great difficulty. Many sorts seem inclined to 

 throw off their flagella when transferred from agar to water. The cover-glasses 

 nurst be clean. When cleaned ready for use seize with the forceps and pass them 

 tliree times through the upper part of the Bunsen flame, with a considerable intei-\'al 

 between each flaming, to avoid cracking. Use a minim quantity of the culture 

 stirred in a big drop of water, or even in 2 to 10 cc. of water in a watch glass or 

 test tube, f iive the bacteria time to diffuse by waiting half an hour or more. Take 

 the cover between the thund) and finger of the left hand, touch the end centimeter 

 of a platinum needle to the water containing the bacteria, and sweep it deftly across 

 the cover glass. In this wa)' the fluid is spread in a very thin sheet o^•er nearly the 

 whole surface of the co\'er and is dry almost at once, with the bacteria well separated. 

 If the fluid will not spread, then the cover is not clean and .should be discarded. 

 The bacterial sheet may be mordanted and stained at once, or first fixed b}' gentle heat. 

 To avoid scorching, the cover should be held between thumb and finger when it is 

 passed rapidly through the flame. Beginners usually burn the bacterial layer. 



