There are a number of other bovine diseases such as anthrax,[100] lockjaw,[101] and hydrophobia[102] in which it has been shown that the virus of the disease is at times to be found in the milk supply, but often the milk becomes visibly affected, so that the danger of using the same is greatly minimized.
There are also a number of inflammatory udder troubles known as garget or mammitis. In most of these, the physical appearance of the milk is so changed, and often pus is present to such a degree as to give a very disagreeable appearance to the milk. Pus-forming bacteria (staphylococci and streptococci) are to be found associated with such troubles. A number of cases of gastric and intestinal catarrh have been reported as caused by such milks.[103]
DISEASES TRANSMISSIBLE TO MAN THROUGH INFECTION OF MILK AFTER WITHDRAWAL.
Milk is so well adapted to the development of bacteria in general, that it is not surprising to find it a suitable medium for the growth of many pathogenic species even at ordinary temperatures. Not infrequently, disease-producing bacteria are able to grow in raw milk in competition with the normal milk bacteria, so that even a slight contamination may suffice to produce infection.
The diseases that are most frequently disseminated in this way are typhoid fever, diphtheria, scarlet fever and cholera, together with the various illy-defined intestinal troubles of a toxic character that occur in children, especially under the name of cholera infantum, summer complaint, etc.
Diseases of this class are not derived directly from animals because cattle are not susceptible to the same.
Modes of infection. In a variety of ways, however, the milk may be subject to contaminating influences after it is drawn from the animal, and so give opportunity for the development of disease-producing bacteria. The more important methods of infection are as follows:
1. Infection directly from a pre-existing case of disease on premises. Quite frequently a person in the early stage of a diseased condition may continue at his usual vocation as helper in the barn or dairy, and so give opportunity for direct infection to occur. In the so-called cases of "walking typhoid," this danger is emphasized. It is noteworthy in typhoid fever that the bacilli frequently persist in the urine and in diphtheria they often remain in the throat until after convalescence. In some cases infection has been traced to storage of the milk in rooms in the house where it became polluted directly by the emanations of the patient.[104] Among the dwellings of the lower classes where a single room has to be used in common this source of infection has been most frequently observed.
2. Infection through the medium of another person. Not infrequently another individual may serve in the capacity of nurse or attendant to a sick person, and also assist in the handling of the milk, either in milking the animals or caring for the milk after it has been drawn. Busey and Kober report twenty-one outbreaks of typhoid fever in which dairy employees also acted in the capacity of nurses.
3. Pollution of milk utensils. The most frequent method of infection of cans, pails, etc., is in cleaning them with water that may be polluted with disease organisms. Often wells may be contaminated with diseased matter of intestinal origin, as in typhoid fever, and the use of water at normal temperatures, or even in a lukewarm condition, give conditions permitting of infection. Intentional adulteration of milk with water inadvertently taken from polluted sources has caused quite a number of typhoid outbreaks.[105] Sedgwick and Chapin[106] found in the Springfield, Mass., epidemic of typhoid that the milk cans were placed in a well to cool the milk, and it was subsequently shown that the well was polluted with typhoid fecal matter.