42 THE BACTERIOLOGICAL EXAMINATION OF MILK 



Add, immediately before use, one per cent, of potassium iodide 

 to the melted gelatine. 



23. Milk : [a) sterile milk, {b) sterilised milk — 



{a) Sterile milk. — No great difficulty need be experienced in 

 obtaining sterile milk direct from the udder of the normally 

 healthy cow. Such milk is a more favourable medium for the 

 growth of bacterial flora than that in which the process of sterili- 

 sation by heat has produced chemical or physical change. With 

 the simple apparatus figured on Plate 7, the authors have for 

 some years past found no difficulty in holding ready to hand a 

 constant supply of sterile milk in its natural condition. The 

 apparatus, which is shown both in the position of drawing milk, 

 and with the milk stored ready for drawing off into tubes or 

 flasks as required, consists of a Kitasato filtering flask of 2 litres 

 capacity, fitted with a two-hole india-rubber stopper, and with 

 the lateral orifice plugged lightly with cotton-wool. Through 

 one of the holes in the cork is led a curved glass tube as shown, 

 reaching in the interior to within a quarter of an inch of the 

 bottom of the flask, and a short length of india-rubber tubing, 

 fitted with a screw pinchcock, connects the terminal curve with 

 a further length of straight glass tube reaching on the outside to 

 within about 2 inches from the bottom level of the flask. (After 

 the milk is drawn, this tube can be fitted, in order to minimise 

 the risk of air contamination when drawing off the milk into test 

 tubes, with a one-holed india-rubber stopper, and a small lamp 

 glass of sufficiently large capacity to allow of the insertion into 

 it from below of an ordinary test tube.) 



Through the second hole of the neck stopper is led a short and 

 right-angled length of glass tubing, projecting into the flask for 

 about I inch, and connected up, at the other end, with about 2 

 inches of " vacuum tubing " fitted in the centre with a screw pinch- 

 cock. The end of this tubing is covered with loose fitting coverings 

 of white wrapping paper tied on with string, and the whole appara- 

 tus is then ready for sterilisation. 



The milking tube and accessories consist of a 3-foot length of india- 

 rubber tubing fitted at one end with an ordinary silver plated " milk- 

 ing tube " such as is supplied by all veterinary instrument makers,^ 



^ A better form still is the tube supplied with the apparatus for injecting 

 a solution of potassium iodide into the udder in the case of milk fever in cows, 

 and which can be procured from Messrs Arnold & Son, veterinary instrument 

 makers, Smithfield. 



