14 DROPS OP WATER. 



sively of species of the most beautiful colours, 

 such as Pandorina, Gonium, &c. A shining film 

 of various colours is also occasionally seen on 

 standing water : this is composed of Infusoria ; a 

 red appearance being often given to water by some 

 species, and by others a yellowish hue. Sheets 

 of water often assume an intense green, from the 

 presence of many of these minute bodies. Lakes 

 have been known to change their colour very 

 mysteriously, and to have caused some alarm in 

 the superstitious ; but it is now known to arise 

 from Infusoria, as they are attracted to the sur- 

 face by the sun in the middle of the day, 

 and descend as that luminary declines ; thus the 

 lake will be clear, morning and evening, and 

 turbid, or of different colours, in the course of 



