472 MILK 



mastitis streptococci. In addition, they usually appear in long 

 chains. There seems also to be some relation between the num- 

 ber of leukocytes in the milk and the length of chains formed by 

 streptococci. When large munbers of leukocytes and long- 

 chained streptococci appear the microscopic picture is fairly 

 characteristic. A smear made from centrifugal sediment from 

 mastitis milk forms a reasonably certain guide for further investi- 

 gation, and in most cases leads to discovery of one or more ani- 

 mals with acute mastitis in the suspected herd. The amount of 

 sediment is naturally large when pus resulting from an udder 

 infection is in the milk. The Trommsdorff method is based on 

 this fact, and is a fairly rehable guide if foreign matter can be ex- 

 cluded from the centrifugal sediment (Figs. 194-196). 



Of course, milk which precipitates a sediment of this na- 

 ture contains different strains of streptococci, though mastitis 

 streptococci are present in abundance if the disease has pro- 

 gressed beyond the initial stages. Isolating streptococci from the 

 sediment may lead to erroneous conclusions. Very careful study 

 of the strains isolated is necessary, and with our Umited knowl- 

 edge of streptococci it is difficult to know which strain is really 

 responsible for the disease in the cow. Pathogenicity for experi- 

 mental animals is not a safe guide, since pathogenicity for one 

 species furnished no proof of pathogenicity for other species. 

 When mastitis milk is injected into guinea-pigs it frequently causes 

 lesions, but not invariably. In fact, about as many guinea-pigs 

 are affected as remain without untoward results, and among the 

 former. Bacillus coli infection is as frequent as streptococcus 

 infection. This shows that streptococci which are highly virulent 

 for cows have but limited pathogenic powers for guinea-pigs. 

 Milk from severe cases of mastitis has been fed to guinea-pigs 

 without the slightest effect beyond that of furnishing food. 



If lactic streptococci can adapt themselves to a protein diet 

 and then become virulent, it is not impossible that the same 

 streptococci which cause common souring of milk may be the cause 

 of mastitis if some accidental lesion in the udder affords them a 

 foothold. Indeed, Mathers has shown that injections of cultures 

 of Streptococcus lacticus into the milk-ducts of a cow did produce 

 a mastitis, although it was of relatively hght natm-e and of short 

 duration. It is evident, then, that innocent streptococci may 

 become virulent. Passing from one cow to another, they may 

 gradually acquire virulence. As a rule lactic streptococci are 

 scarce in the udder, but there are cases on record where they were 

 present in large numbers. When this happens udder diseases 

 are not necessarily the consequence, but an udder lesion caused 

 by accident or ill treatment may give the disease a start. 



