[65] Bull. 128, Wis. Expt. Stat., Sept. 1905.

[66] Freudenreich, Landw. Jahr. d. Schweiz, 1896, 10; 1.

[67] Weigmann, Milch Zeit., 1890, p. 881.

[68] Conn, 3 Rept. Storrs Expt. Stat., 1890, p. 158.

[69] Freudenreich, Fuehl. Landw. Ztg. 43: 361.

[70] Harrison, Bull. 120 Ont. Agr'l. Coll., May, 1902.

[71] Milch Zeit. 22:569.

[72] Marshall, Bull. 146, Mich. Expt. Stat., p. 16.

[73] Grotenfelt, Milch Zeit., 1889, p. 263.

[74] Menge, Cent. f. Bakt., 6:596; Keferstein, Cent. f. Bakt., 21:177.

[75] Heim, Arb. a. d. Kais. Gesundheitsamte, 5:578.

[76] Adametz, Milch Zeit., 1890, p. 225.

[77] 12 Rept. Wis. Expt. Stat., 1895, p. 148; also Bull. 67, Ibid.,
June, 1898.

CHAPTER V.

RELATION OF DISEASE-BACTERIA TO MILK.

Practical experience with epidemic disease has abundantly demonstrated
the fact that milk not infrequently serves as a vehicle for the
dissemination of contagion. Attention has been prominently called to
this relation by Ernest Hart,[78] who in 1880 compiled statistical
evidence showing the numerous outbreaks of various contagious diseases
that had been associated with milk infection up to that time. Since
then, further compilations have been made by Freeman,[79] and also by
Busey and Kober,[80] who have collected the data with reference to
outbreaks from 1880 to 1899.

These statistics indicate the relative importance of milk as a factor in
the dissemination of disease.

The danger from this source is much intensified for the reason that
milk, generally speaking, is consumed in a raw state; and also because a
considerable number of disease-producing bacteria are able, not merely
to exist, but actually thrive and grow in milk, even though the normal
milk bacteria are also present. Moreover the recognition of the presence
of such pathogenic forms is complicated by the fact that often they do
not alter the appearance of the milk sufficiently so that their
presence can be detected by a physical examination. These facts which
have been experimentally determined, coupled with the numerous clinical
cases on record, make a strong case against milk serving as an agent in
the dissemination of disease.

~Origin of pathogenic bacteria in milk.~ Disease-producing bacteria may be
grouped with reference to their relation toward milk into two classes,
depending upon the manner in which infection occurs:

Class I. Disease-producing bacteria capable of being transmitted
directly from a di