1912.] 



Ropy Milk. 



1003 



Additional Characters. — In milk the capsule is very marked, and 

 is sometimes as thick as the length of the organism; but in most 

 cases is only one-third the thickness of the rod. 



Ward has noted a great difference in the size of individual organ- 

 isms when grown in bouillon culture, and also that in this case the two 

 ends of the rods are more darkly stained (bipolar staining). 



The bacilli are readily stained ty aniline dyes, also by Gram's 

 stain and by haemotoxylin. 



The method of Gabbi (26) and Welche's glacial acetic acid method 

 are recommended for the staining of the capsule. 



Large involution forms are frequently observed in old cultures ; 

 they often resemble yeasts in size and shape. 



Comparison of the Characters of Various Ropy Milk Organisms. 



It will be seen on looking up the thousands column that ropy milk 

 organisms differ very much in size and shape. 



There is, however, a considerable tendency to variation between 

 individual organisms of the same kind, this being very marked in 

 bouillon cultures. Many of the organisms produce involution forms, 

 so that very fresh cultures should always be prepared before making 

 slides for the purpose of identification. 



The tendency to form chains and the length of the rods are very 

 variable. 



From the hundreds column it will be seen that spore formation 

 is as a rule absent. Special care must be taken in examining Bacillus 

 viscosus, which, according to Conn, gives the appearance of spores 

 with double staining. 



x-\lthough different members of the group vary greatly as regards 

 motility (see ten's column), the character is not a very reliable one for 

 the purpose of identification. If, however, fresh cultures on agar 

 are made daily for a week and kept at an optimum temperature 

 motility should be observed in the seventh culture, if the organism 

 possesses the property. The culture should be examined when 

 8 to 16 hours' old. 



The cause of ropiness (see unit column) is a fundamental difference, 

 which, as mentioned above, can be used for purposes of classification, 

 but it does not serve to distinguish between the many organisms 

 which owe their ropiness to a swollen capsule. 



It is evident from the first decimal place that most of these organ- 

 isms are more or less aerobic; the organisms in Group I., being 

 " obligate aerobes/' with one or two exceptions. 



The liquefaction of gelatine (second place of decimals) is a valuable 

 property for the purposes of identification, but in some cases the 

 liquefaction takes place very slowly; Micrococcus mucilagindsus only 

 liquefies gelatine in three weeks. ' 



The variation in this respect between the individual members of 

 Group I. indicates very fundamental differences in the chemical action 

 of these organisms on the nitrogenous constituents of milk, and work 

 in this direction would probably bring into greater prominence the 

 differences between the organisms of this group. 



The numerical system fails to do justice to the method of distin- 



3 Z 2 



