220 AIDS TO BACTERIOLOGY 



Salty Milk may be watery (1027 to 1029 specific gravity). 

 It is stated to occur only in connection with inflammation 

 of the udder. It is detected by taste, its high percentage 

 of ash, and by its low percentage of milk-sugar. Accord- 

 ing to Klenze, 2-4 per cent, of small deposits of calcium 

 carbonate in the milk glands may give rise to sandy milk. 



White Mould. See O'idium lactis, p. 17. 



For practical purposes, it may be said that any milk 

 which goes sour rapidly is a bad milk, although the con- 

 verse is not necessarily true. According to Schatzmann, 

 if a sample of milk be kept for twelve hours at 40 C., and 

 within that time coagulates, it is to some extent defective, 

 and in nine hours no change whatever should appear to 

 have occurred. The presence of colostrum is a ground 

 for the condemnation of milk; it can usually be detected 

 by the presence of long, elastic, yellowish threads. 



Sterilisation. Fractional sterilisation is too lengthy a 

 process for use commercially, so recourse is had to Pas- 

 teurisation (see 'Aids to the Analysis of Food and Drugs') 

 i.e., the milk is heated to 62 or 68 C. for thirty minutes.* 

 This kills all, or nearly all, the pathogenic bacteria that 

 are likely to be present in milk, but also destroys the 

 lactic acid bacteria. After pasteurising, the spore- 

 forming bacteria which will escape develop, unchecked 

 in the absence of lactic acid bacteria, and may turn the 

 milk rotten, often with no outward sign of its condition. 

 For this reason milk once pasteurised should be consumed 

 within eighteen or twenty-four hours i.e., before sporu- 

 lating bacteria have had time to multiply to an objection- 

 able extent. Pasteurisation affords milkmen a con- 

 venient method of preserving surplus milk till the follow- 

 ing day, but the period during which milk remains in 

 a house is so short that, as a general rule, probably twenty - 

 four hours do not elapse between Pasteurisation and 

 consumption. 



Reporting on the electrical treatment of milk as applied 

 by E. W. Hope, Beattie says that there is a reduction in 

 content of bacteria of 99-25 per cent., and colon and 

 tubercle bacilli are destroyed. 



* See also p. 60. Sir John McFadyean (Veterinary Congress, 1914) 

 also advocates raising milk to 85 C., and considers there is evidence, 

 already ample in amount, that milk so treated is from a nutritive 

 point of view in no way inferior to uncooked milk. 



