430 
brane of infants is very susceptible to bacteria and their products, 
and a large proportion of the summer complaints of infants has 
been traced to the use of bacteria-laden milk. As we grow older 
it seems that the gastro-intestinal mucous membrane becomes 
comparatively immune, or resistant to bacterial action. 
If milk were a transparent fluid the enormous growth of bacteria 
found in market milk would be plainly visible to the naked eye. 
A similar amount of bacterial growth in broth, gelatine, beer, jelly, 
or other clear substance, would render such food unsightly, and it 
would be generally regarded as unfit for use on account of the evi- 
dence of fermentative and putrefactive changes. 
The number of bacteria in milk is not so important from a public 
health standpoint as the kind and nature of the bacterial products. 
But wdth cleanliness and the liberal use of ice the total number of 
bacteria can be kept down, and this affords a mode of protection 
against the dangerous species and their toxic products. Milk con- 
taining few bacteria will contain proportionately few or no harmful 
varieties. Most of the specific pathogenic bacteria which some- 
times contaminate milk, grow best at the body temperature and 
not at all at the low temperatures at which milk must be kept in 
order to keep the total bacterial count dovm. 
Park® raises the question — 
Are even these enormous numbers of bacteria in milk during hot weather actually 
harmful? Here we have only to refer to uniA-ersal clinical experience, that a great 
number of children in cities sicken on the milk supplied in summer, that those put on 
milk which is sterile or contains few bacteria as a rule mend rapidly, while those kept 
on the impure milk continue ill or die. 
Our knowledge is probably as yet insufficient to state just how many bacteria must 
accumulate to make them noticeably dangerous in milk. Some varieties are un- 
doubtedly more harmful than others and we have no way of restricting the kinds that 
will fall into milk except by enforcing cleanliness. AVe have also to consider that 
milk is not entirely used for some twelve hours after being purchased, and that during 
all this time bacteria are rapidly multiplying, especially where, as among the poor, no 
provision for cooling it is made. Slight changes in the milk which to one child would 
be harmless would in another produce disturbances which might lead to serious dis- 
ease. A safe conclusion is that no more bacterial contamination should be allowed 
than it is practical to avoid. Any intelligent farmer can use sufficient cleanliness and 
apply sufficient cold, with almost no increase in expense, to supply milk twenty-four 
to thirty-six hours old which will not contain in each cubic centimeter over 50,000 
to 100,000 bacteria, and no milk containing more bacteria should be sold. 
Judged by the colonies that develop upon agar plates, the number 
of bacteria in milk increases every time it is handled. Separator 
milk contains more than the original milk. The same is true of 
filtered milk. Milk strained through gauze or cotton, or filtered 
oPark, W. H.: The great bacterial contamination of the milk of cities, can it be 
lessened by the action of health authorities? Journ. Hyg. , vol. 1, 1901, p. 391. 
