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 Spirillum. 

 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 



Fig. 65. Ophidomonas sanguinea of 

 stagnant water (slightly magnified). 



Fig. 66. Protococcus nivalis of 

 red snow (magnified). 



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 



