182 
The peritoneum and mesentery are studded with nodules. The 
mesenteric glands are swollen and may contain purulent or caseous 
matter. The liver is covered with nodules and patches which may 
be raised above the liver substance or may penetrate into the liver 
parenchyma. The spleen is sometimes only enlarged; at other times 
thickly studded with nodules. The kidneys show yellowish patches. 
The lungs are covered with small transparent nodules which do not 
penetrate into the lung tissue. The sternal lymphatic glands are 
swollen, but show no caseation. Numerous bacilli can be demon- 
strated in these lesions. Many animals after injection show con- 
siderable signs of illness during the first fourteen days, with diminu- 
tion in weight, and then recover. Pure cultures of this bacillus 
are only pathogenic for guinea pigs (but not always) ; rabbits 
and white mice are immune. After intraperitoneal inoculation of 
guinea pigs some die in from four to eight weeks, with considerable 
emaciation, and show the following post-mortem appearances: At 
the seat of inoculation there is a purulent infiltration containing 
the characteristic bacilli; also peritonitis, varying in intensity from 
a flocculent fibrinous exudation to strong connective tissue adhesions. 
The mesentery is studded with small nodules ; the . glands are en- 
larged, but not caseous; there are patches on the liver, and miliary 
nodules throughout an enlarged spleen. The thoracic cavity and or- 
gans are often almost exempt from lesions. Infected animals do not 
react to tuberculin. Histologically the nodules in the liver and 
spleen consist of a collection of lymphoid elements with but very 
few epithelioid and multinuclear cells. The bacilli are found in the 
middle of a young nodule, toward the periphery if caseation has 
commenced. The typical giant cells of tuberculosis do not occur. 
More often — especially after inoculation with butter containing 
the pseudo-tuberculosis bacilli — the nodules appear to consist of a 
central necrosed portion surrounded by a leucocytic infiltrated area. 
COLLECTION OF SAMPLES AND TECHNIC. 
The samples of milk were all collected and brought to the Hygienic 
Laboratory by an inspector of the health department of the District 
of Columbia. Usually a pint bottle, though sometimes a quart, with 
the paper cap untampered with was obtained either from the diary 
or delivery wagon. The bottle was at once placed on ice by the col- 
lector and usually reached the laboratory in about one hour after 
collection. A few samples were obtained from some of the hospitals 
and charitable institutions of the District. The milk and cream were 
well mixed by vigorously shaking the bottle. The sample for plat- 
ing was taken out with a sterile pipette, and then 50 cubic centimeters 
of the mixed milk was put into a large sterile centrifuge flask. To 
