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. 11a. This may be compared with fig. 12, in which the same organism is 
shown without capsules. Fig. 114 shows the extreme viscidity of a culture due to 
the formation and deliquescence of capsules. Fig. 13 shows the tenuous threads 
into which Bacillus tracheiphilus may be drawn as it oozes from the cut stems of 
cucurbits. Fig. 14 is a detail from the same more highly magnified, the viscid con- 
necting substance being unstained. 
FLAGELLA. 
Ehrenberg was the first to describe flagella on bacteria (Bacterium triloculare, 
1838). Nothing more was done until 1872, when Cohn discovered them on .Sfz- 
rillum volutans. In 1875 Dallinger & Drysdale saw and figured them on Bacterium 
termo. In 1875 Warming determined their existence on Vibrio rugula and Sfr- 
rillum undula. \n 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 termo and also on Spirdllum volutans. After 1879 no one 
appears to have disputed their existence. In 1890 Messea proposed to divide the 
flagellate 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 and 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 very 
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 readily 
from cultures grown for some days in a very dilute Uschinsky’s solution—1 to 3 
drops in 10 ce. 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 
must be clean. When cleaned ready for use seize with the forceps and pass them 
three times through the upper part of the Bunsen flame, with a considerable interval 
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. Give the bacteria time to diffuse by waiting half an hour or more. ‘Take 
the cover between the thumb 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 way the fluid is spread in a very thin sheet over nearly the 
whole surface of the cover 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 by 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. 
8 eee ae 
