80 MIOKO-OEGANISMS IN WATER 



Detection of Anaerobic Micro-organisms in Water 



In the various methods of water-examination de- 

 scribed above, only those microbes, of course, which 

 are capable of growing in the presence of air will be 

 ■discovered, whilst for the investigation of anaerobic 

 forms, which onty flourish in the absence of free oxygen, 

 the methods described on pp. 35, 38 must be employed. 

 Particularly well adapted for such investigations is the 

 method of placing an ordinary Esmarch-tube cultiva- 

 tion inside a larger closed tube containing potassium 

 pyrogallate. 



It must of course be borne in mind that there are 

 many bacteria which grow both in the presence and in 

 the absence of free oxygen, so that such microbes will 

 give rise to colonies both in the aerobic and anaerobic 

 ■cultures , 



Photographic Eecord of Plate-cultures 



A very simple and effective method of photo- 

 graphically reproducing the appearances of gelatine- 

 plate cultures of bacteria may be mentioned before 

 closing this chapter. It has been devised by De Giaxa,^ 

 and the accompanying figure gives some idea of the 

 results obtained. 



When the plate has been incubated for a sufficient 

 length of time it is removed from the moist chamber, and 

 its under-surface is carefully wiped with blotting-paper 

 soaked in ether, in order to remove all traces of moisture. 

 The plate is then placed on a piece of albuminised paper 

 rendered sensitive by means of silver nitrate, just as is 

 used in ordinary photographic operations. In order to 



' ' Ueber eine einfache Methode zur Beproduction der Koch'schen 

 Kulturplatten,' Centralblatt filr Bakteriologie^ vol. iii., 1888, p. 700. 



