356 Messrs Purvis and Black, Oxygen content of the river Cam 
masses of bacteria when floating or suspended in water resembled — 
flakes of shredded paper or pieces of cotton wool in size from — 
a three-penny piece to a two-shilling piece. They were con- 
stricted at one end, the point of attachment of the growth; the — 
Dissolved 
oxygen taken The 
up in 5 days rainfall | 
in grams per _ in 
100,000 inches - 
—-—-- dissolved oxygen absorbed in five days in grams per 100,000. 
rainfall in inches during the four days previous to that on which the sample 
» was taken. 5 
Fig. 1. Curves showing the degree of pollution as indicated by the rise and fall of 
the amount of oxygen absorbed in five days by the river Cam 150 feet above the 
effluent outfall, and its relation to the rainfall. 
other end and body of the mass was spread out fan-wise, and 
when held up to the light resembled frost on a window-pane. — 
Microscopically they consisted of long chains of rod-shaped 
