4. Elsner's Medium. This special potassium-iodide-potato-gelatine medium is used for the examination of typhoid excreta. It is made as follows: 500 grams of potato gratings are added to 1000 cc. of water; stand in cool place for twelve hours, and filter through muslin; add 150 grams of gelatine; sterilise and add enough deci-normal caustic soda until only faintly acid; add white of egg; sterilise and filter. Before use add half a gram of potassium iodide to every 50 cc. Upon this acid medium common water bacteria will not grow, but Bacillus typhosus and B. coli flourish.
5. Parietti's Formula consists of—phenol, five grams; hydrochloric acid, four grams; distilled water, 100 cc. To 10 cc. of broth 0.1–0.3 cc. of this solution is added. The tube is then incubated in order to see if it is sterile. If that is so, a few drops of the suspected water are added, and the tube reincubated at 37° C. for twenty-four hours. If the water contains the B. typhosus or B. coli, the tube will show a turbid growth.
6. Widal's Reaction. Mix a loopful of blood from a patient suspected of typhoid fever with a loopful of young typhoid broth culture in a hanging drop on a hollow ground slide. Cover with a cover glass and examine under 1/6-inch objective. If the patient is really suffering from typhoid, there will appear in the hanging drop two marked characteristics, viz., agglutination and immotility. This aggregation, together with loss of motility, is believed to be due to the inhibitory action of certain bacillary products in the blood of patients suffering from the disease. The test may be applied in various ways, and its successful issue depends upon one or two small points in technique into which we cannot enter here, but which the reader will find dealt with in the appendix.
7. Flagella-staining. Special methods must be adopted for staining the flagella of Bacillus typhosus and B. coli. The cover glasses should be absolutely clean, the cultures young (say eighteen hours old), and a diluted emulsion with distilled water must be made in a watch-glass in order to get bacilli discrete and isolated enough. Van Ermengem's Method is as follows:—Place a loopful of the emulsion on a clean cover glass and dry it in the air, fixing it lastly by passing it once or twice through the flame of a Bunsen burner. Place films for thirty minutes in a solution of one part boric acid (2 per cent.) and two parts of tannin (15.25 per cent.), which also contains four or five drops of glacial acetic acid to every 100 cc. of the mixture. Wash in distilled water and alcohol. Then place for five to ten seconds in a 25.5 per cent. solution of silver nitrate. Immediately thereafter, and without washing, treat the cover glass to the following solution for two or three seconds: gallic acid, five grams; tannin, three grams; fused potassium acetate, ten grams; distilled water, 350 cc. After this place in a fresh capsule of silver nitrate until the film begins to turn black. Wash in distilled water, dry, and mount. The process contracts the bacilli somewhat, but the flagella stain well.
The Bacillus coli communis occupies such an important place in all bacteriological investigation that a few words descriptive of it are necessary in this place. The "colon bacillus," as it is termed, appears to be almost ubiquitous in distribution. The idea once held that it belonged exclusively to the alimentary canal or sewage is now discarded. It is one of the most widely distributed organisms in nature, though, as its name implies, its habitat is in the intestinal tract of man and animals. It is an aërobic, non-sporulating, non-liquefying bacillus, about .4 µ in thickness, and twice that measurement in length; hence it often appears oval or egg-shaped. Its motility is in varying degree, occasionally being as active as B. typhosus, but generally much less so. It possesses lateral flagella. On gelatine plates at 20° C. B. coli produces non-liquefying, greyish-white, round colonies; in a stroke culture on the same medium, a luxuriant greyish band, much broader and less restricted to the track of the needle than B. typhosus. In depth of medium or "shake" cultures there is an abundant formation of bubbles of gas (methane or carbon dioxide) in the medium. On potato it produces a light yellow, greasy growth, which must be distinguished from the growth of B. fluorescens liquefaciens, B. pyocyaneus, and several other species on the same medium. If the potato is old or alkaline, the yellow colour may not appear. Milk is curdled solid in from twenty-four to forty-eight hours, and a large amount of lactic acid produced. In broth it produces a uniform turbidity, with later on some sediment and a slight pellicle. It gives the reaction to indol.
It is now the practice to speak of the family of Bacillus coli rather than the individual. The family is a very large one, and shows throughout but few common characters. The morphology readily changes in response to medium, temperature, age, etc. Fermentation of sugar, coagulation of milk, or indeed the indol reaction cannot always be used as final tests as to whether or not the organism is B. coli, for unfortunately some members of the family do not show each of these three features. Most varieties, however, appear to show some motility, a small number of flagella, a typical growth on potato, and develop more rapidly on all media than B. typhosus. These characters, plus one or more of the three features above named, are diagnostic data upon which reliance may be placed.
Cholera. This word is used to cover more a group of diseases rather than one specific well-restricted disease. In recent years it has become customary to speak of Asiatic cholera and British cholera, as if indeed they were two quite different diseases. But, as a matter of fact, we know too little as yet concerning either form to dogmatise on the matter. Until 1884 practically nothing was known about the etiology of cholera. In that year, however, Koch greatly added to our knowledge by isolating a spirillum from the intestine and in the dejecta of persons suffering from the disease.
Cholera has its home in the delta of the Ganges. From this endemic area it spreads in epidemics to various parts of the world, often following lines of communication. It is a disease which is characterised by acute intestinal irritation, manifesting itself by profuse diarrhœa and general systemic collapse, with cramps, cardiac depression, and subnormal temperature. The incubation period varies from only a few hours to several days. In the intestine, and setting up its pathological condition, are the specific bacteria; in the general circulation their toxic products, bringing about the systemic changes. Cholera is generally conveyed by means of water.