_Micro-pathology._ Typhoid fever is an infiltration and coagulation, necrosis, and ulceration of the Peyer's patches in the small intestine of man. The mesenteric glands show the same features, except that there is no ulceration. The spleen is enlarged, and contains the germs of the disease in almost a pure culture. The bacillus is present in the intestinal contents and excreta, particularly so when the Peyer's glands have commenced ulceration. In the blood of the general circulation the bacillus is not demonstrable, except in very rare instances. Typhoid fever is not, like anthrax, a blood disease. COMPARATIVE FEATURES OF BACILLUS TYPHOSUS AND B. COLI B. TYPHOSUS B. COLI _Morphology:_ Cylindrical bacillus Shorter, thicker; filaments rare. 2.4 µ, unequal lengths; some filaments. _Flagella:_ Long, wavy, spiral, Shorter, stiffer, fewer; movement and very numerous; movement very less active. active. _On Gelatine and Agar:_ Angular, Even edge, homogeneous; much irregular, raised colonies; slow larger, quicker growth, and less growth; translucent; medium translucent than _B. typhosus_; remains clear. medium becomes turbid or coloured. _In Gelatine:_ In ordinary Under the same circumstances gelatine and in sugar gelatine abundant gas is produced. no gas is produced. _Milk:_ Not curdled by the Milk is coagulated (within three bacillus. days). _Indol:_ The production of indol Indol is present. in ordinary broth is _nil_. _Potato:_ The "invisible growth," Thick, yellow growth. if potato is acid. _Lactose:_ Fermentation very slight. Fermentation marked. _25 per cent. Gelatine at 37° C.:_ Gelatine remains limpid and clear, Strongly and uniformly turbid but possesses thick pellicle. (Klein). _Elsner's Iodised Potato Gelatine:_ Very fast growth; larger, brown, Slow growth; small, very less transparent colonies. transparent colonies. _Widal's Test:_ Bacilli become Bacilli remain actively motile. motionless and clumped together when suspended in a drop of blood serum from a typhoid patient. _Broth containing 0.3 per cent. Phenol Grows well. or Formalin_ (1:7000): No growth. _Thermal Death Point:_ 62° C. for five 66° C. for five minutes (Klein). minutes (Klein). _Vitality in Water and Sewage:_ The _B. coli_ retains for a much longer Typhoid bacillus soon ceases to time its vitality and power of multiply and readily dies (Klein). self-multiplication (Klein).