458 
of whom insist that advantage may be taken of this property for the 
preservation of milk without the use of ice. 
When we stop to consider that bacteria frequently enter the imper- 
fectly closed orifice of the teat and grow in the milk contained in 
the milk cisterns, and that they often invade the finer tubules of the 
gland structure where the milk is being freshly secreted, we must 
be convinced that the “ germicidal ” power of milk must be exceed- 
ingly feeble, if it exist at all. 
This property varies with the milk of different animals, and also 
in the milk of the same animal at different times. 
There is evidence to show that the restraining action of fresh raw 
milk upon the growth of bacteria varies with the bacterial species, 
and when we inquire into the causes of the phenomenon we find that 
this is what we might expect. 
When micro-organisms are transferred to a strange medium they 
sometimes hesitate, until they become sufficiently accustomed to the 
new T surroundings, before they begin to multiply. Our experiments 
show that this is by no means always the case and can not account 
for the facts now under consideration. 
We know that the serum of milk may contain “ antibodies ” in 
appreciable and variable quantity similar to those found in the 
blood. For instance, diphtheria, tetanus, and other antitoxins have 
been demonstrated in the milk of immunized animals. We might 
also expect small quantities of the agglutinating, bactericidal, and 
bacteriolytic substances present in blood serum to pass into the milk 
serum. Agglutinins in milk would apparently diminish the number 
of bacteria contained therein when estimated by the number of 
colonies that develop on agar plates. This might occur even though 
the number of bacteria present were actually increased. Microscopic 
examination of the bacteria in milk made at once after milking, and 
again in eight hours, demonstrates that such agglutination actually 
takes place. This is confirmed by our other technique. 
We know that milk always contains large numbers of leucocytes — 
many of them of the polymorphonuclear variety. These are known 
to be phagocytes, and we might assume that they are active in milk 
for a short time after it is drawn. In fact we have found that some 
of the leucocytes actually contain more bacteria after eight hours 
than when the milk is freshly drawn. 
If phagocytosis played a part in the diminution in the number of 
bacteria in milk, we must assume that the milk serum has opsonic 
power.® Our work shows that phagocytosis plays no essential role 
in the apparent reduction in the number of bacteria in fresh milk. 
a In fact Woodhead and Mitchell claim to have demonstrated opsonins in milk. 
Jonrn. of Path, and Bactr., vol. 11, 1906-^7, p. 408. 
