THE RELATION OF MICROORGANISMS TO MILK. 313 



crease in numbers. Many of the organisms in this group are chromogenic, 

 orange and lemon yellows being among the more common forms. They 

 are mostly cocci and do not liquefy gelatin. From the standpoint of the 

 commercial milkman these organisms are of little significance and this is 

 probably also true from the standpoint of the consumer. 



THE CASEIN-DIGESTING OR PEPTONIZING BACTERIA. These organ- 

 isms digest the casein either with or without coagulation. Many of them 

 coagulate the casein with an alkaline reaction. They liquefy gelatin. 

 Most of the organisms of this group are rods of various shapes and sizes, 

 some of them being the largest rods found in milk. Some are motile and 

 some non-motile. Some representatives of this group produce little or no 

 odor, but many of the species develop very strong putrefactive odors. 

 Barny or cowy odors or other off-flavors sometimes found in milk and dairy 

 products are caused by the action of this type of organisms. They are 

 associated with filth and their presence in milk indicates unsanitary con- 

 ditions of production or handling. 



PATHOGENIC ORGANISMS. This group of organisms produces no 

 changes in the milk which would indicate their presence. Some of them 

 do not even develop in milk, as is the case with the Bad. tuberculosis 

 Others, as the diphtheria bacteria and typhoid fever bacilli, may grow in 

 milk with great rapidity. This group also contains certain species which 

 produce diarrhoeal disorders, especially in infants and young children. 

 Some of them are probably organisms which are also included in the 

 peptonizing group of organisms. The specific pathogenic organisms, 

 possibly with the exception of Bad. tuberculosis, get into milk, either 

 directly or indirectly, from human patients suffering with the particular 

 disease. 



FACTORS INFLUENCING THE DEVELOPMENT OF MICROORGANISMS IN MILK. 



The number of microorganisms found in fresh milk shows its bacterial 

 condition at that time, but it gives little idea of the organisms which may 

 be found in the same milk at later periods. There are many factors to be 

 considered if we wish to study the development of the various types 

 which get into ordinary milk. These factors may be considered briefly 

 under the following heads: 



INITIAL CONTAMINATION. Fresh milk varies widely in the number of 

 organisms which it contains as a result of the conditions under which it 



