BAI TERIOLOfJICAL EXAMIXATIOX. 293 



and quantities of about 1 c.c. placed io Durham tubes, which are 

 plugged with cotton wool, and sterilised. 



Sugar Mr<lia. — The sugars used are glucose, lactose, and 

 cane sugar ; other carbohydrates, such as dulcitol, adonitol, 

 and inuCn, may be also used, but the three sugars give a fairly 

 good distinction between the organisms of intestinal origin. 



These media are made up, containing 7 "5 per cent, gelatine, 

 2 per cent, peptone, 1 per cent. Lemco, and 1 per cent, of the 

 sugar ; they are heated till clear, filtered, 1 c.c. of 5 per cent, 

 potash solution added, and the media tinted blue with litmus. 

 Quantities of about 1 c.c. are placed in Durham tubes, five of 

 the small tubes being held together by an india-rubber band, 

 and contained in a 3-inch X 1-inch pluui-'f^d test tube. Thev 

 are sterilised as usual. 



Milk TMfees.— Plugged test tubes, each containing 10 c.c. of 

 separated milk, are sterilised. 



It is a convenience to plug tubes containing the various media 

 with different coloured cotton wool ; this saves labelling, and 

 minimises the chance of error. The use of different coloured 

 cotton wool also serves to distinguish different quantities of 

 water taken. 



Prepare also a number of test tubes, each containing 9 c.c. of 

 distilled water ; plug these with cotton wool : and sterilise. 

 The tubes containing nutrient media and sterilised water must 

 be covered with a rubber cap to prevent evaporation. 



Procedure. — Sterilise a pipette delivering 1 c.c. by heating to 

 150° C. (350° ¥.) ; the pipette is l)est sterilised in" a test tube 

 plugged with cotton wool. .\s soon as this is cool, open the 

 bottle containing the sample, and take out 1 c.c. Add this to 

 one of the tubes containing sterilised water and replace the 

 plug immediately. Take out another 1 c.c. and add this to a 

 tube of nutrient gelatine, which should have been previously 

 liquefied and allowed to cool to 'iT' C. (80 F.). Pour into a 

 sterilised Petri dish. 



With another sterilised I c.c. pipette add 1 c.c. of the mixture 

 of water with sterilised water to a tube of nutrient gelatine, 

 which has been previously liquefied by heating and cooled to 

 about 27 C. (80' F.), and pour into a Petri dish. 



The Petri dishes should be placed in an ice chest to solidify 

 the gelatine. Place the gelatine cultivations in an incubator 

 kept at about 22 C. (or 72 F.) ; after two and a-half days the 

 number of colonies that have developed are counted. 



If the water is suspected to be bad, smaller amounts of water 

 may bo taken, 1 c.c. of the diluted water being added to 9 c.c. 

 of sterile water. If it is supposed that the water is good, the 

 amounts taken may be inerea.sed. The quantities given will, 



