128 MICROBES, FERMENTS, AND MOULDS. 
1836, in a stream near Jena, and which he named Ophi- 
domonas jenensis, or sanguinea (Fig. 65). It is, on 
account of its form, now placed in the genus Spirillwm. 
Like many other plants, it readily passes from green 
to red. No one is surprised by the green scum 
which covers reservoirs in summer, since it is so 
common; but when this colour changes, often in a 
single night, and passes from green to red, the unaccus- 
tomed tint excites wonder, although it is caused by 
d 
"MBcnsnt pater (slgntly maguited. Mie red snow (nsguilied). 
the same plant which was green the day before. If 
there is a thunderstorm or waterspout which draws 
up the red water from the ponds and reservoirs, and 
discharges it in the form of rain on the surrounding 
country, we hear of the phenomenon that it rains blood, 
and it would be easy to find in the drops of rain the 
reddish microbe which imparts this colour to them. 
In northern regions the snow is often tinged with 
the colour of blood by an analogous Micrococcus, which 
