1912.] 



Ropy Milk. 



993 



words, are strongly aerobic, growing mostly on the surface of the 

 milk or in the cream layer. None of these organisms produce much 

 acid, and many produce no acid, while others produce an alkaline 

 reaction in the milk. 



To another group (Group II.) belong organisms which do not 

 dissolve the casein, but precipitate it by means of the acid they 

 produce. The casein in this state helps to thicken the slimy substance 

 produced, and is not afterwards dissolved. The organisms of this 

 group are able to grow much better without air than the other type. 

 They therefore grow through the entire mass of the milk or whey. 



Certain ordinary lactic bacteria sometimes acquire the property 

 of forming slime, and must therefore be included in this group. They 

 are sometimes the cause of sliminess in "starters" used in creameries 

 and cheese factories. In the manufacture of Edam cheese a ropy 

 starter, called " lange wei," is sometimes used in Holland. It is 

 very persistent when introduced into a dairy, and makes cheese of 

 very uniform quality. 



Adametz (i) has suggested that the ropy milk organisms may 

 be classified according to the nature of the slime-producing substance. 

 In this method of classification the first and largest group (Group i) 

 consists of those organisms which produce slimy milk as a result 

 of the swelling of the outside layers of the cell membrane, which, 

 becoming sometimes thicker than the diameter of the organism, 

 makes a sticky capsule, which adheres to solid substances and also 

 causes the organisms to stick together. 



A study of the characters given in the unit column of the pro- 

 perties of the organisms (see table in appendix) shows that nearly 

 all the organisms in Group I. come under this head, these being 

 harmless from a dietetic point of view. The ropy cell wall has a com- 

 position resembling cellulose, and has in some instances been identified 

 as dextrin. 



An exception to the harmless nature of these organisms is Bacillus 

 Guillebeau (c), which also owes its slime-producing properties to a 

 swollen capsule, but must be classed separately because it comes from 

 diseased udders, and must be regarded as pathogenic or disease- 

 producing. 



The members of the second group (Group 2) owe their ropiness to 

 the production of a slimy protein substance, which is also harmless. 

 The chief organism in this group is the whey coccus, which plays an 

 important part in the making of some varieties of Edam cheese. 



The third group (Group 3) which Adametz suggests, contains 

 only one known member (Bacillus viscosus L, van Laer). This 

 organism owes its ropiness to a nitrogen-containing substance, which, 

 however, is not a protein. 



In some other cases, as with the organisms more generally known 

 as lactic ferments, and in cultures in which ropiness may not always 

 be observed, the cause is more probably due to the enormous number 

 of bacteria developed in the medium than to any specific slimy 

 material produced. 



Not Injurious to Health. — With the exception mentioned 

 above, ropy milk caused by bacteria is not injurious to health, 



