IDENTIFICATION OF BACTERIA IN MILK 6S7 
Identification of Bacteria in Milk.— The bacterial types found in 
milk may he very \arie(l; the opportunity for contamination does 
not cease when the milk is drawn from the cow— every step in the 
handling of the milk from the producer to the consumer offers new 
avenues for infection. A catalogue of all the bacteria which have 
been isolated from milk would be very extensive, but of little i)ractical 
value. Of vastly greater importance is the recognition of the patho- 
genic organisms which may be transmitted to man and the chemical 
changes which ordinary saprophytic milk bacteria induce in it. There 
are relatively few bacteria which are pathogenic both for the cow and 
for man. Of these, the bovine tubercle bacillus, the unknown virus 
of foot and mouth disease and the virus of the disease known as 
trembles of cattle are transmissible to man, the latter causing a well- 
defined symptom-complex known as milk sickness. Goats, particularly 
Maltese goats, infected with the specific organism Micrococcus (Bacil- 
lus) melitensis, transmit the disease Malta fever to man through their 
milk.i 
In addition, the ^'iruses of certain infections specific for man may 
be transmitted in milk. These organisms gain entrance to the milk 
directly from human sources, incidental to the various handlings 
which it undergoes, and they may persist in unheated milk in suffi- 
cient numbers to infect the consumers. Typhoid, diphtheria, scarlet 
fever, epidemic sore throat and pseudodiphtheria infection, dysentery 
(bacillary), various types of epidemic diarrhea and even i\.siatic 
cholera are the more important diseases thus transmitted. 
Except in very rare instances, specific pathogenic bacteria other than 
the bovine tubercle bacillus and Micrococcus (13acillus) melitensis have 
not been isolated directly from milk. The evidence of the transmis- 
sion of pathogenic bacteria through infected milk rests largely upon 
statistical data. It is very conclusive, however, and many severe 
epidemics of typhoid fever and other infections have been satisfac- 
torily traced to carriers or mild cases of the same disease among those 
who have undoubtedly handled the milk. 
Conradi,- however, appears to have isolated the typhoid bacillus from 
infected milk which was shown to be responsible for a small outbreak 
of typhoid fever, and Bruck'' and others have shown that typhoid 
ba^cilli and similar pathogenic bacteria may persist and even multiply 
in the presence of the various microorganisms commonly ])resent in 
ordinarily good grades of milk. 
The virus of foot and mouth disease and the bovine tubercle bacillus 
have been detected in butter and cheese prepared from milk containing 
these viruses. 
' The detection of tubercle bacilli in milk has been discussed in the chapters on Tuber- 
culosis and Bacillus abortus. Malta fever has been discussed in the chapter on Bacillus 
melitensis and foot and mouth disease in the section relating to Filterable viruses. 
= Centralbl. f. Bakteriol., orig., 1906, 40, .31. 
3 Deutsch. med. Wchnschr., 1903, 29, 460. 
