DISEASE GERMS IN MILK. 163 
Scarlet Fever and Diphtheria. There is positive evidence that 
these two diseases may be distributed by milk and that some 
epidemics are attributable to the milk-supply. The cause of scarlet 
fever is yet uncertain, and it is not known whether cows can contract 
the disease and then produce milk already contaminated, or whether, 
as in typhoid fever, the contamination of the milk is wholly secondary. 
A few epidemics of scarlet fever have been traced to the cow with more 
or less certainty, and it is beyond doubt also that the milk may 
become infected with the cause of this disease by secondary 
contamination. The farmer should, therefore, take 
precautions to prevent any person from working in 
the dairy who is recovering from scarlet fever. 
Diphtheria is produced by a well-known bacillus 
(Fig. 41). Here again there seems some doubt whether 
cows have the disease. It is certain, however, that the diphtheria bac~ 
milk may become secondarily infected through con- 
valescent diphtheria patients working in the dairy and handling the 
milk. Some instances of diphtheria have been traced to such a cause. 
Diarrheal Diseases. Besides the diseases mentioned, milk 
is responsible for a portion of those obscure diseases characterized 
by diarrheal troubles, which are especially prevalent in warm 
weather. Among these are cholera infantum, which is responsible 
for the death of so many children, and summer complaint, which is 
less serious. These troubles are not yet so well understood as the 
others we have mentioned. They do not appear to be caused by 
any single specific bacterium, but are probably due to the excessive 
multiplication of a number of certain kinds of bacteria in the milk. 
That they are due to milk bacteria is proved by the facts that (i) 
they occur most frequently at the seasons of the year when milk 
bacteria are most numerous; (2) they are more prevalent among in- 
fants fed upon cow's milk than among breast-fed children. What 
kinds of bacteria are at fault in the production of these diseases 
we do not know. Quite a number of bacteria are found in milk 
which produce poisonous secretions and which may be agents in 
the production of these obscure diseases. For the purpose of 
our discussion it is sufficient to state that they are probably due 
