the mycelium condenses into elongated portions. In older cultures of nocardias many coc- coid cells are changed into resistant cells. The latter are larger than the vegetative coccoid cells; the plasma of these cells is thicker than the plasma of vegetative cells; on fresh media they germinate like the spores of actinomycetes; they form 2 to 3 germ tubes. Besides the cells mentioned, numerous involution forms can often be found in older cultures of nocar- dias; the cells are thin, regularly cylindrical or coccoid and are often transformed into a series of spherical or elliptical ampules and a club-like form (2 to 3 microns and more). The multiplication of nocardias proceeds by fission and budding; occasionally they form special spores. Budding occurs often. The buds are formed on the lateral surface of the cells; when they have reached a certain size, they fall off and develop into rod-shaped cells or filaments. The spores are formed by the breaking up of the cell plasm into separate por- tions usually forming 3 to 5 spores; every portion becomes rounded, covered with a mem- brane and is transformed into a spore; the membrane of the mother cell dissolves and dis- appears. The spores germinate in the same way as those of actinomyces. They form germ tubes which develop into a mycelium. The colonies of nocardias have a paste-like or mealy consistency and can easily be taken up with a platinum loop; they spread on glass and occasionally render the broth turbid. The surface colonies are smooth, folded or wrinkled. Typical nocardias never form an aerial mycelium, but there are cultures whose colonies are covered with a thin coating of short aerial hyphae which break up into cylindrical oidiospores. Examination by fluorescent microscopy after treatment with carbol-auramin and decolor- izing with NaCl-HCl-ethyl alcohol can reveal acid-fast species or their e.xudates (Richards, Stain Technol., 18, 1943, 91). Many species of nocardias form pigments; their colonies are of a blue, violet, red, yellow or green color; more often the cultures are colorless. The color of the culture serves as a stable character. Krassilnikov (Ray fungi and related organisms, Izd. Akad. Nauk, U.S.S.R., Moskau, 1938) divides the genus into two groups: 1) Well developed aerial mycelium; substrate my- celium seldom produces cross-walls; the threads break up into long, thread-like rods; branches of the aerial mycelium produce segmentation spores and oidiospores; the latter are cylindrical with sharp ends; no spirals or fruiting branches. This group is the same as group B of Jensen (op. cit., 1931, 345). 2) Typical forms; mycelium develops only at early stages of growth, then breaks up into rod-shaped and coccoid bodies; smooth and rough colonies, dough-like consistency; never form an aerial mycelium; similar to bacterial colo- nies; aerial mj^celium may form around colonies. This genus can also be divided, on the basis of acid-fastness, into two groups: Group 1) Partially acid-fast organisms which are non-proteolj^tic, non-diastatic and utilize paraffin; usuallj^ yellow, pink, or orange-red in color. Group 2) Non-acid-fast organisms which are diastatic, largely proteolytic and do not utilize parafiin; yellow, orange to black in color. The type species is Nocardia farcinica Trevisan. Key to the species of genus Nocardia. I. Partially acid-fast* organisms with strongly refractive cells; non-proteolytic and gen- erally non-diastatic; constantly capable of utilizing paraffin. A. Initial mj^celium fully developed, well branching, dividing into rods and generally into cocci. 1. Vegetative mycelium soft, without macroscopically visible aerial mycelium. a. Vegetative mycelium yellow, orange or red. b. Pathogenic.
- Acid-fastness is not marked in cultures, is apparent in infected tissues and is pronounced
in sputum or other exudates.
