68 DAIRY BACTERIOLOGY 



B. THE ABNORMAL FLORA 



The changes brought about by the normal flora in milk cannot 

 be looked on as defects unless they appear at too early a stage. 

 Thus the fact that milk turns sour on standing is in itself not a 

 defect, but if the milk arrives at the dairy in a sour condition it is 

 certainly defective. Defects of milk we understand to be not the 

 normal but the abnormal changes. Defects of milk may be 

 spoken of as primary if present from the outset, or secondary if 

 they appear at a later stage in the history of the sample. In the 

 former case they may simply be due to changes to which the milk 

 is naturally subject at different stages of the period of lactation, 

 or they may originate from the fodder or diseases of the cows ; 

 in the latter case they will be due to the action of microorganisms 

 which find their way into the milk either during the milking or at 

 a later stage. 



Primary Milk Defects. It is well known that just after 

 calving or towards the end of the period of lactation the milk is 

 abnormal in composition and coagulates badly with rennet. While 

 colostrum has a strongly acid reaction, milk obtained towards the 

 end of the lactation period is rather neutral than acid. Owing 

 to the rapid growth of the foatus, much potash and especially 

 phosphoric acid are used up instead of passed into the milk. On 

 the other hand, the percentage of sodium chloride often increases 

 to such an extent that the milk tastes salt or bitter salt. It may 

 be pointed out that so long as the cow is not in calf, the milk may 

 be suitable for cheese making during two to three years 1 . 



The feed may have an undesirable effect on the milk by impart- 

 ing to it an abnormal taste and smell, the best known examples 

 being a taste of onions through feeding with onions, a turnip- like 

 taste through giving liberal amounts of turnips and swedes, 

 mustard and rape seed cake containing mustard, and a bitter 

 taste from lupins (unboiled) or large amounts of vetches. Further- 

 more, poisonous substances may be derived from certain plants 

 which, however, are generally avoided by the cows when on 

 pasture. Greater danger attaches to such poisons as iodine, 

 arsenic and mercury compounds which may be given as medicines 

 and thus passed into the milk. For this reason no milk should be 

 sent from any farm where the cows are given medicine of any 

 kind, without the sanction of a veterinary surgeon. Similarly, 

 disinfectants such as carbolic acid may pass through the blood 

 into the milk, or they may be absorbed direct from the air, in 

 which case the milk will also be unsuitable as food. Finally the 



1 Orla Jensen, " Landwirtschaftliches Jahrbuch der Schweiz," 1905, 

 p. 542. 



