be added to a bouillon culture of actively motile typhoid bacilli, the bacilli lose their motility and

FIG. 80.-Bacillus typhosus: superficial colony two days old on a gelatin plate; × 20 (Heim).

FIG. 81.-Bacillus coli: superficial colony two days old, on a gelatin plate; × 21 (Heim).

soon aggregate in clumps. Dilutions of serum I 10 and 1: 30 with a half-hour time-limit are

those most commonly employed. In doubtful cases a dilution of I: 100 with a one-hour time-limit is recommended.

(a) Place 9 drops of a twenty-four-hour bouillon culture of actively motile typhoid bacilli on separate

FIG. 82.-Bacillus typhosus, from an agar culture six hours old, showing the flagella stained by Löffler's method; × 1000 (Fränkel and Pfeiffer).

spots on a clean cover-glass. Add I drop of serum from the blood of the suspected typhoid case,' mix

1 The blood may be collected in a capillary tube and after coagulation the serum removed; or dried blood may be moistened with water and the resulting solution used as serum. The latter method, however, does not permit accurate dilution. Chester and Robin have recently devised a pipet for delivering a measured drop of blood, so that dilu

all together, and mount as a hanging-drop preparation.'

(b) Examine with the inch or with the oil

a

FIG. 83.-The Chester and Robin pipet for delivering uniform drops of blood for the Widal test. A glass and rubber pipet, the bulb of which is enclosed between two strips of metal held in place by a Hoffman clamp.

immersion lens. If the case is one of typhoid, after some time, varying between a few seconds and a

tions may be made with a fair degree of accuracy from dried blood. It consists of an ordinary medicine-dropper of a given size, the bulb of which is enclosed on either side by two narrow strips of metal (Fig. 83, c, c.), and both placed in a medium-sized Hoffman clamp. The inward movement of the clamp by means of the screw a compresses the bulb, while a slight turn in the opposite direction dilates it a little and permits a small drop of blood to enter. In expelling the blood the dropper is held vertically over a strip of thick filter-paper, and the clamp is slowly compressed until a single drop falls of its own weight. This drop is then dried, and when the test is to be applied the blood-spot is cut from the paper and drops of the diluting fluid are added from an exactly similar pipet until the required dilution is reached.

1 It is convenient to use a slide on which two glass rings have been cemented, so that one may be used as a control, containing the culture of bacilli alone.

half-hour, the bacilli will be seen to become less motile, and finally to cease all movement and

FIG. 84.-Slide with two cells for observing Widal reaction with a control.

appear in clumps here and there throughout the field.

V.

a

b

FIG. 85.-Widal reaction: a, bouillon culture of Bacillus typhosus; b, the same after the addition of typhoid

serum.

This reaction can be reversed and made to serve as a means of identifying the typhoid bacillus if the serum of a person known to have typhoid fever is at hand.

10

FIG. 86.-Bacterium pneumoniæ, from the heart's blood of a rabbit; × 1000 (Fränkel and Pfeiffer).

1. Study the morphology and biology of cultures of B. pneumoniae and B. pneumonicum.

2. Make cover-glass preparations from pneumonia sputum. Stain in Löffler's methylene-blue or carbol-fuchsin, diluted one-half.

3. Prepare sections of lung-tissue from cases of