For example, if one wishes to identify a short, peritrichous. Gram-negative, non-spore-forming, non-chromogenic rod that grows well on ordinary culture media at 37°C., fermenting glucose and lactose with the production of acid and gas, not liquefying gelatin, with negative reaction for acetylmethylcarbinol, citrate-negative, alginate-negative, pectinase-negative, producing indole and reducing nitrates, consult the key to the orders on page 33.
In this key examine I: Cells rigid. Motile by means of polar flagella or non-motile. This does not indicate our organism, which is peritrichous. We turn next to II: Not as above. Under A: Cells rigid. Spherical or straight, rod-shaped cells. Occur singly, in chains or in trichomes. Motile by means of peritrichous flagella or non-motile. These characters agree with those of the organism in question.
We turn now to 1, in the same key: Cells spherical or rod-shaped. No trichomes, though chains of cells may occur. This indicates that the organism in question belongs in Order IV, Eubacteriales.
In the key to the families of Order Eubacteriales, p. 281, examine I: Cells rod-shaped. Gram-negative. This indicates the organism in question, so we turn next to A: Aerobic or facultatively anaerobic, which again indicates the organism in question.
The next entry, 1: Large, ovoid to rod-shaped cells, sometimes yeast-like in appearance. Free-living in soil. Fix free nitrogen, does not indicate the culture under study so we turn to 2: Not as above.
The heading, 2: Heterotrophic rods which may not require organic nitrogen for growth. Usually motile, with one to six flagella. Frequently form nodules or tubercles on roots of plants or show violet chromogenesis. Colonies usually large and slimy, especially on mannitol agar, does not indicate the organism in question. We then turn to aa: Not as above.
Heading b: Straight rods which grow readily on ordinary peptone media. May of may not ferment sugars anaerobically with the production of organic acids again indicates the culture under study.
The heading c: Glucose usually attacked oxidatively or not at all does not indicate the organism in question as it is an active fermenter of glucose and lactose, cc: Ferment glucose anaerobically, frequently producing visible gas from glucose, and sometimes lactose indicates that the culture under study belongs in the Family IV, Enterobacteriaceae.
We now turn to the key to the tribes of family Enterobacteriaceae, page 334. In this key we examine I: Lactose fermented anaerobically, usually within 48 hours. This indicates the culture under study.
The entry A: Prodigiosin not produced also indicates the non-chromogenic organism in question. Likewise, 1: Do not produce protopectinase. Not parasitic on plants also applies to our culture, so we turn to the key to the genera of Tribe I, Escherichieae, page 335.
We turn now to I: Alginic acid is not decomposed with the production of acid and gas. This likewise indicates the organism is question. Under this, A: Lactose is fermented within 48 hours also indicates the culture under study, as does 1:
