THE HAY BACILLUS 



17 



small quantity of hay in water for somewhat less than a 

 hour. After boiling, the liquid is left to stand for a 

 time, and it is not long before B. subtilis, the Hay 

 Bacillus,- makes its appearance in great numbers. 

 Needless to say, we cannot study the organism without 

 a high-power microscope, for a single isolated cell is but 

 Ys^ixTX) i^ch in diameter, and from five to eight times 

 that extent in length. A satisfactory examination can 

 be made with a combination 

 of lenses yielding magnification 

 of 1,000 diameters. Each cell 

 is seen to have a distinct cell- 

 wall. The cell-contents com- 

 pletely fill their investment, 

 and for a time the cell is in 

 active movement, the move- 

 ment being due to the lashing 

 of flagella (see Fig. 7, a), which 

 are not apparent unless the 

 organism is stained by a process 

 familiar to microscopists. The 

 Bacillus is observed to multiply 

 rapidly by repeated fission. But 

 in a few days the cells seem to 

 get tired of their hitherto ceaseless activity; they rise 

 to the surface of the water, and rest there in long threads, 

 the cells being connected end-to-end. At the same time 

 the cell-walls become gelatinous, and the organisms 

 form a gelatinous mass, known as the zoogloea stage, 

 on the surface of the liquid (Fig. 7, e). As long as the 

 conditions are favourable for growth, the cells continue 

 to multiply by division, but when the food-supply in 



3 



Fig. 7. — BAcaaxtrs subtiijs. 

 a, d. Ciliated motile cell and 

 filament; 6, non-motile cells 

 and filament ; e, zoogloea, 

 X 175 ; c, cells and endo- 

 spores from the zoogloea; 

 a-d, X1050. 



