MICROBIC CHANGES IN MILK. 589 



rennet, and are capable of coagulating enormous quantities of milk. 

 After a certain time, they also secrete a second diastase, viz., casease, 

 ^Yhich. acts in the ripening of cheese. 



Clotted Milk. — This term is used in dairies to indicate milk which 

 coagulates in lumps immediately after being withdrawn from the udder, 

 or which coagulates spontaneously a few hours later. 



The change may be of a chemical nature, depending on conditions 

 of keep or feeding. More frequently, however, it is related to a latent 

 non-pathogenic infection of the udder, or to immediate infection of the 

 milk after removal by lactic ferments contained in the milk vessels or 

 the atmosphere. 



It is necessary, according to circumstances, either to modify the diet 

 or disinfect the milk vessels, and immediately pasteurise the milk. 



Milk without Butter. — Less commonly the diseased condition is 

 indicated by marked diminution in the quantity of cream. 



Churning only produces a poor kind of butter, particles of which do 

 not readily cohere. This peculiarity is due to the presence of micro- 

 organisms, which have not yet been fully identified. It can be prevented 

 by disinfection of the milking vessels, as well as of the dairy itself, and 

 by the use of centrifugal separators. 



Putrid Milk. — This milk is characterised by its odour. It cannot be 

 used for making butter. In fact, as soon as the cream separates, little 

 bubbles of gas form at various points and break, leaving small cavities. 

 These little separate cavities reunite very rapidly, and the cream becomes 

 reabsorbed as fast as it is formed. Afterwards oily drops formed of 

 butyric, capric, and caprylic acids appear in the depressions and give 

 the milk a repulsive odour (rancidity). 



This change is seen during mammitis, but most commonly results 

 from uncleanliness in byres and dairies. In the latter case putrefaction 

 occurs about twenty-four hours after milking, and is due to the growth 

 in the milk of Bacterium termo, lineola, etc. These organisms are pre- 

 sent in the dust which falls into the milking pails in the byre ; when 

 milk so contaminated is stored in the dairy the changes occur. 



Putrid odour may also be due to the presence of ammoniacal gas 

 in the byre, or to special toxins liberated by microbes which have found 

 their way into the milk. It is most marked during the warm seasons of 



the year. 



The occurrence of putrid milk can be prevented by disinfecting the 

 dairy and the milking pails daily for a certain time. 



Mucous, Yiscous, or thready Milk. — These terms are applied to a 

 condition which usually appears twenty-four or thirty-six hours after the 

 milk has been withdrawn. The milk seems thick and viscous, and can 

 be drawn out into threads like mucus. It sticks to neighbouring objects, 



