THE KINDS OF MICRO-ORGANISMS IN MILK 381 



part was added to 200 parts of the milk to be used. Recent 

 studies, however, have shown that Streptococcus hollandicus is 

 t a variety of Str. lacticus, and that by the use of pure cultures 

 of Str. lacticus an equally good product can be obtained. The 

 consequence is that lange wei is now not in general use. Str. 

 lollandicus forms viscous milk only at moderate temperature of 

 about 20 C., and when cultivated at higher temperature it causes 

 souring of milk without slime formation. 



It has been repeatedly reported that when strains of Strepto- 

 coccus lacticus are cultivated for successive generations in milk 

 they not infrequently acquire the ability to produce slimy milk. 

 This fact has been particularly annoying when butter starters 

 are propagated. Slimy or ropy milk is difficult to handle for 

 butter and cheese making, and is, therefore, undesirable from this 

 point of view. Furthermore, the slimy or ropy condition some- 

 times develops slowly, so that the milk is delivered to consumers 

 in apparently good condition, but shows evidence of an objec- 

 tionable character after standing for some time. 



Slimy or ropy milk has been observed in many parts of the 

 world, and it must be taken for granted that the organisms which 

 produce this abnormal condition are widely distributed. Some 

 authors make distinctions between slimy, ropy, and stringy 

 milk. The term "ropy milk" is used to designate milk that can 

 be drawn out into long threads, which is not possible with slimy 

 milk. Stringy milk, according to some authors, applies only to 

 milk from diseased udders. The milk then contains fibrin and 

 large numbers of body cells which cause the stringy condition. 

 The definition of stringy milk implies, therefore, that bacteria 

 are only indirectly responsible for the abnormal condition by being 

 the cause of the pathologic condition, while in ropy or slimy milk 

 bacteria are directly responsible by attacking some of the milk 

 constituents, with production of slimy or ropy substances. 



The effect of different organisms, or different temperatures, or 

 of other, at present unknown, conditions is such as to cause a dif- 

 ferent degree of viscosity. The viscosity can be measured by 

 comparing the length of time required for a definite amount to 

 be discharged from a pipet, or by allowing the milk to flow down an 

 inclined pane of glass. Sometimes, however, the viscosity is so 

 intense that the milk will not flow at all, and a tube containing 

 such milk can be inverted without spilling the contents. 



Some organisms producing viscosity in milk grow chiefly at 

 the surface, so that lower portions of the milk are not as intensely 

 slimy as upper portions, while other organisms produce an equal 

 degree of viscosity throughout. Usually slime is formed at a 

 moderate temperature of about 20 C., while at higher tempera- 



