TEXT-BOOK OF BACTERIOLOGY. 167 



depth of the punctui-e, but principallj^ in the upper portion, in 

 which also the pigment is developed. . In advanced cultures the 

 great mass of bacteria has sunk and lies at the bottom, while the 

 upper portion of the culture has become quite clear. 



On agar the orange sarcina produces a very beautiful golden- 

 yellow, shining crust; on potatoes it grows slowly, producing, how- 

 ever, its characteristic pigment. 



It is also strictly aerobic, and does not thrive, or but very im- 

 perfectly, in the incubator. 



Lastly, a red sarcina is, perhaps, worthy of mention, since it has 

 been found by Menge that it can under some circumstances be the 

 cause of a reddening of milk under natural conditions. 



The sarcina in question is a rather large one, which on the gel- 

 atin plate slowly forms colonies of moderate extent. These grad- 

 ually liquefy the culture medium to a very slight degree. They 

 form an intense rose-colored pigment, which appears in scratch 

 cultures on oblique agar, on potatoes with alkaline reaction, and 

 particularly in sterilized milk. This latter becomes, at length, so 

 strongly colored that one might fairly call it " red milk." In non- 

 sterilized milk, which usually falls a speedy prey to lactic-acid 

 fermentation, the red sarcina is unable to thrive. 



It is a strictly aerobic micro-organism and ceases to grow al- 

 most entirely at the temperature of the incubator. 



Bacillus Megateritjm. 



Bacillus megaterium, so named by De Bary, who first described 

 it, and which is of interest for us because De Bary employed it in 

 his important investigations concerning spore-formation and the 

 sprouting of spores, is a species of bacteria. 



Megaterium was first discovered, by pure accident, on the leaves 

 of boiled cabbage, but it develops without difficulty on our ordinary 

 food media. 



It is clearly a rod, about three times as long as it is broad, of 

 clumsy appearance, with strongly -rounded corners, frequently some- 

 what bent, so that it has also been called the " large comma bacil- 

 lus." 



Peculiar to it is the granulation of the cell-contents, which, un- 

 like those of most other bacteria, do not appear evenly transparent 

 and homogeneous, but covered with little granules and dark spots, 

 showing differences in the state of contraction of the protoplasm 

 for which we can give no explanation. 



The Bacillus megaterium has a strong inclination to produce in- 



