112 MICRO-ORGANISMS IN WATER 



Thus, as far as the bacterial contents of lakes has 

 been investigated, their waters appear to contain a 

 remarkably small number of micro-organisms, which 

 is what we should anticipate also, considering the op- 

 portunities which are offered for prolonged subsidence. 

 Lakes should thus generally contain fewer micro- 

 organisms than the streams which supply them, and 

 this expectation was recently verified in a striking 

 manner by one of us in the case of the Loch of Lin- 

 trathen, referred to above, and the two principal burns 

 which enter it, thus : — 



Inzion Btirn, just above where it enters Lintratben, 



June 10, 1893, contained 1,700 bacteria per c.c* 

 Melgam Burn „ „ ,, „ 780 ,. 



Water issuing from Lintrathen „ ,, 30 „ 



The phenomenon is the more significant from the 

 fact that chemically the w^aters of the burns were dis- 

 tinctly superior to that of the loch, the greater part of 

 the loch water having doubtless been derived from 

 these streams when they were both chemically and 

 bacterially much inferior to what they were at the time 

 of the collection of the above samples, which was during 

 a prolonged and almost unprecedented drought, a coii- 

 dition most favourable to the purity of such streams. 



Sea-water. — The bacterial contents of sea-water is 

 a subject of obvious interest, but one on which but 

 very little information was until recently available. 

 Even now, practically, the whole extent of our know- 

 ledge is based upon the results obtained by two investi- 

 gators, De Giaxa^ and Eussell,^ both of whom conducted 

 their experiments in the Gulf of Naples. 



De Giaxa, whose investigations only incidentally in- 

 cluded some determinations of the number of bacteria 



1 Zeitschrift filr Hygiene, vol. vi. 1889, p. 186. 



2 Ihid. vol. xi. 1891, p. 177. 



