INFLUENCE OF DISEASE UPON MILK 111 
Considering the frequency of the catarrhal and paren- 
chymatous forms of mastitis in dairy cows, cases of 
illness in man resulting from the ingestion of milk from 
cows affected with this disease have not been reported as 
often as would be expected. There are several reasons 
for this. The milk from a diseased cow may be diluted 
with milk from cows in normal condition to such an extent 
as to render the mixed milk harmless. Furthermore, 
some of the mastitis bacteria have a relatively low 
virulence for man. Finally, it rarely happens that the 
physician is able to establish the connection between the 
disease in his patient and the cow affected with mastitis, 
even when milk from the latter is the cause of the disease. 
Nevertheless, there are on record numerous cases of ill- 
ness in man caused by the ingestion of milk from cows 
affected with mastitis, the symptoms in these cases being 
nausea, vomiting, and diarrhoea, sometimes associated 
with fever, faintness, languor, and cramps in the legs. In 
two instances the milk which was the cause of the disease 
had been boiled. It is not known whether the illness in 
these cases was due to a heat-resisting toxin or to bacteria 
which survived the heat because of the protection fur- 
nished by the membrane which forms on the surface of 
milk when it is heated. 
Numerous epidemics of septic sore throat have been 
reported in which the infection was transmitted by milk. 
In some of these epidemics, cows affected with strepto- 
coccic mastitis were found to be the source of the infec- 
tion, but in the other outbreaks the circumstances seemed 
to point to the infection of the milk by dairy workers suf- 
fering from the disease. To account for the persistence of 
streptococci for several days in the milk supplies involved 
in the second group of epidemics, the theory has been 
