in the blood, the periodicity of the symptoms, their amenability to quinine, together with the character of the prevailing epidemic, generally combine to guide to a correct diagnosis.
The detection of the comma bacillus in the stools is now regarded as a positive indication of cholera. It would be rash, however, to affirm that a negative result from bacteriological examination of a single case is conclusive against its being cholera. Moreover, such" examinations to be trustworthy have to be made by a skilled bacteriologist. According to Kanthack and Stephens, the following were the methods of bacteriological diagnosis practised by Klein during the threatened epidemic in 1893:—
Method 1.— A. flake from the dejecta is placed in peptone broth and incubated at 37° C. In twenty-four hours an abundant crop of vibrios is found in the superficial layers of the broth. This pellicle consists of a practically pure culture, or, at any rate, is a culture which easily allows of pure subcultures being obtained.
Method 2.— A flake is placed in sterile salt solution or broth; it is shaken up, and from this gelatin or agar tubes are inoculated, and plates are made. In agar plates incubated at 37° C. numerous colonies may be found in twenty to thirty hours. In the gelatin plates, after two to three days' incubation at 20° to 22° C., numerous typical colonies can be got. (A more modern method which is very efficacious is Dieudonne's blood-alkali agar. Equal parts of defibrinated ox-blood and normal caustic soda solution are mixed with 70 c.c. of neutral peptone agar. On this medium few organisms other than the cholera vibrio develop.)*[1]
Method 3.— A flake is placed directly into Dunham's peptone salt solution (1 per cent, peptone, 0.5 per cent, sodium chloride), or the Dunham's solution is inoculated after previous dilution of the material. The peptone solution, after six, eight, to ten hours' incubation at 37° C., shows a definite turbidity, due to the rapid growth of the comma bacilli; and the cholera-red reaction may be obtained, although not absolutely specific. For speedy diagnosis this method is most valuable; in six to twelve hours, or, at latest, in sixteen hours, comma bacilli can be found in the superficial layers of the
- ↑ * The cholera vibrio forms indol very rapidly and in considerable amount, reducing nitrates to nitrites, especially in peptone water. A few drops of pure sulphuric acid added to a peptone-water culture eight to twelve days old gives a pinkish colour, more intense according to the age of the culture. The coli group and other bacteria produce indol, but do not reduce nitrates to nitrites so readily; the presence of the latter is essential for the reaction.
