539 
if milk was a homogenous liquid like water and not an emulsion. In- 
vestigations made to determine how tubercle bacilli distribute them- 
selves in milk under different conditions proved that they adhere to 
the cream globules with a tenacity that can not be broken by a simple 
difference of specific gravitjq even when this difference is reenforced 
by centrifugalization. The result is, when milk is allowed to stand 
for cream to rise, or when cream is separated from it rapidly in a 
centrifuge, the tubercle bacilli, when they are present, rise as abun- 
danth" with the cream globules as they gravitate with the sediment 
and disappear from the intermediate layer or the skim milk, which 
is practically a homogenous fluid. This holds true when pure cul- 
tures of tubercle bacilli are added to milk and also when the bacilli 
are introduced into it with tuberculous bovine feces, or with pus from 
tuberculous abscesses, and when they are present because of tuber- 
culous lesions in the udder of the cow from which it was obtained. 
These facts almost make it unnecessary to formulate the conclu- 
sion that cream, obtained from tuberculous milk, measure for meas- 
ure, contains more tubercle bacilli than the milk. 
Cream is the material from which butter is made, and that butter 
made from infected cream has the infection transferred to it Avas 
proven by repeatedly making butter from infected cream and test- 
ing it. 
It has been recorded that both strained and unstrained milk to 
which small masses of feces from cows affected with tuberculosis 
were added caused tuberculosis in guinea pigs. Cream from such 
strained and unstrained milk also caused tuberculosis in guinea pigs, 
and butter made from the cream of such strained and unstrained milk 
likewise caused tuberculosis in guinea pigs. 
Visibly affected tuberculous cows and cows affected with udder 
tuberculosis are no doubt a serious menace to public health when 
their milk is used raw in one form or another as human food, but, as 
dairymen are not exceptionally unscrupulous persons and will rarely 
sell milk from a visibly diseased cow, and as udder tuberculosis 
among cows that are not otherwise Ausibl}^ diseased is rare, we may 
conclude that the apparently healthy, tuberculous cow, the cow that 
intermittently expels tubercle bacilli from her body per rectum with 
her feces, is the most important tuberculous danger for public health 
that has its origin in the dairy herd. Such apparent^ harmless, 
actually dangerous cows not only infect their own milk, but also the 
milk of the other coavs stabled Avith them, and, as we haA^e seen, such 
infected milk, both strained and unstrained, equally when it is used 
as a beverage or as cream or as butter contains live virulent tubercle 
bacilli. 
