and streak, to incubate aerobically and carry out further inoculation
experiments with the resulting growths.

EXAMINATION OF MILK.

"One-cow" or "whole" milk, if taken from the apparently healthy animal
(that is, an animal without any obvious lesion of the udder or teats)
with ordinary precautions as to cleanliness, avoidance of dust, etc.,
contains but few organisms. In dealing with one-cow milk, from a
suspected, or an obviously diseased animal, a complete analysis should
include the examination (both qualitative and quantitative) of samples
of (a) fore-milk, (b) mid-milk, (c) strippings, and, if possible,
from each quarter of the udder. "Mixed" milk, on the other hand, by the
time it leaves the retailer's hands, usually contains as many
micro-organisms as an equal volume of sewage and indeed during the
examination it is treated as such.

It is possible however to collect and store mixed milk in so cleanly a
manner that its germ content does not exceed 5000 micro-organisms per
cubic centimetre. Such comparative freedom from extraneous bacteria is
usually secured by the purveyor only when he resorts to the process of
pasteurisation (heating the milk to 65 deg. C. for twenty minutes or to
77 deg. C. for one minute) or the simpler plan of adding preservatives to
the milk. Information regarding the employment of these methods for the
destruction of bacteria should always be sought in the case of mixed
milk samples, and in this connection the following tests will be found
useful:

1. _Raw Milk_ (Saul).

To 10 c.c. milk in a test tube, add 1 c.c. of a 1 per cent. aqueous
solution of ortol (ortho-methyl-amino-phenol sulphate), recently
prepared and mix. Next add 0.2 c.c. of a 3 per cent. peroxide of
hydrogen solution. The appearance of a brick red color within 30 seconds
indicates raw milk. Milk heated to 74 deg. C. for thirty minutes undergoes
no alteration in color; if heated to 75 deg. C. for ten minutes only, the
brick red color appears after standing for about two minutes.

2. _Boric Acid._

Evaporate to dryness, 50 c.c. of the milk which has been rendered
slightly alkaline to litmus, then incinerate.

Dissolve in distilled water, add slight excess of dilute hydrochloric
acid and again evaporate to dryness.

Dissolve the residue in a small quantity of hot water and moisten a
piece of turmeric paper with the solution. Dry the turmeric paper.
_Rose_ or _cherry-red_ color = borax or boric acid.

3. _Forma