2 DEPARTMENT BULLETIN 319 5 U. S. DEPT. OF AGRICULTURE 
milk of varieties of the common lactic-acid group of bacteria, or, 
as in the case of yogurt, by special organisms ; or a yeast may be 
present, adding an alcoholic to the ordinary acid fermentation. 
THERAPEUTIC VALUE OF FERMENTED MILKS 
Fermented milks have been used since very early times, but it is 
only within recent years that physicians in this country have become 
interested in the possibilities of their use for therapeutic purposes. 
This interest was stimulated in a large measure by the work of 
Metchnikoff (60) 2 and his associates. His views, which are set forth 
in some detail in Chapter V of his book entitled " The Prolongation 
of Life," are looked upon by conservative investigators in this 
country as overdrawn and as unsupported by experimental evidence. 
In his book great stress is laid on the longevity of the peoples of cer- 
tain countries in which fermented milks are an important part of 
the diet. In considering evidence of this kind, however, it should 
be remembered that many other things may contribute to the gen- 
eral health and vigor of a people and that these factors can not be 
excluded in drawing conclusions. People who habitually consume 
large quantities of fermented milk usually live a simple life, largely 
in the open air. There is no means of knowing how much this may 
have contributed to the vigorous old age to which they frequently 
attain. 
Sour-milk therapy has recently undergone a new development. 
Evidence already indicates that Lactobacillus acidophilus, which is 
a normal inhabitant of the intestinal tract, is a definite and efficient 
therapeutic agent. Acidophilus milk has been adjudged a practical 
means of bringing about the predominance of this organism in the 
intestinal tract. Upon the advice of physicians, large quantities of 
acidophilus milk are being consumed to combat intestinal disorders. 
The use of fermented milks as a therapeutic agent is based on 
the assumption that they are able to combat the so-called autoin- 
toxication caused by the undue accumulation in the body of toxic 
substances emanating from the intestinal tract. The theory of auto- 
intoxication may be stated briefly as follows : The digestive tract 
of human beings is at birth free from bacteria; but in various ways, 
chiefly through the food, many kinds of bacteria are introduced into 
the alimentary canal. In the intestines, particularly in the large 
intestines, some of them find favorable conditions for growth and 
become established there in large numbers. In the normally nour- 
ished infant the bacterial varieties are limited in number and for 
the most part consist of acid-forming types which, by the active 
fermentation of the milk sugar furnished in large quantities in 
the food, produce conditions under which bacteria of the putre- 
factive type are unable to multiply to any extent. The predominance 
of an acid fermentation in the large intestine produces an acid stool 
with a characteristic but comparatively unobjectionable odor. As the 
child gets older the variety of food is greater, and the relative pro- 
portion of carbohydrate to protein is much reduced. In place of the 
acid fermentation there is a decomposition of the protein by other 
2 Figures in parentheses refer to the bibliography at the end of this bulletin. 
