Waksman — 26 — Actinomycetes 



them measuring 0.7-0.8[x, according to the species. The mycehum is 

 not septate. The further development of nocardias, however, differs 

 from that of streptomyces cultures: the filaments soon form a transverse 

 w^all and the whole mycelium breaks up into regularly cylindrical short 

 cells, then into coccoid cells. On fresh culture medium the coccoid 

 cells germinate into the mycelium. The whole cycle in the develop- 

 ment of nocardias continues 2 to 7 days. Most frequently the coccoid 

 cells are formed on the third to the fifth day, but those of certain species 

 (Nocardia ruber, for example) can be found as early as the second day. 



Numerous chlamydospores are sometimes found in older cultures of 

 Nocardia. They are formed in the same way as the chlamydospores in 

 true fungi; the plasma inside the filaments of the mycelium condenses 

 into elongated portions. In older cultures of Nocardia many coccoid 

 cells are changed into "durable" forms. The latter are larger than the 

 vegetative coccoid cells, and the plasma of these cells is thicker than the 

 plasma of vegetative cells. On fresh media the so-called "durable" cells 

 germinate like the spores of Streptomyces. They form 2 to 3 germ tubes. 

 Besides the cells mentioned, numerous involution forms can often be 

 found in older cultures of Nocardia. These 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 more than 3[i). 



The multiplication of nocardias proceeds by fission, budding, and 

 rarely by special spores. Budding occurs often. The buds are formed 

 on the lateral surfaces 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 3 to 5 in number. Every portion becomes rounded, 

 covered with a membrane, and transforms into a spore; the membrane 

 of the mother cell dissolves and disappears. The spores germinate in the 

 same way as those of Streftomyces; they form germ tubes which develop 

 into a mycelium. 



The colonies of nocardias have a paste-like or mealy consistency and 

 can be easily taken up with a platinum loop. They spread on the glass 

 and occasionally render the broth turbid. The surface colonies are 

 smooth, folding, or wrinkly. 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 oidio- 

 spores. 



Many nocardias form pigments. Their colonies are of a blue, violet, 

 red, yellow, and green color. More often the cultures are colorless. 

 The color of the culture serves as a stable character. 



Krassilnikov (234) divided the genus Nocardia into two groups: 



]. Well developed aerial mycelium— substrate mycelium seldom produces cross 

 walls; the threads break up into long thread-like rods; branches of aerial mycelium 

 produce segmentation spores and oidiospores, the latter being cylindrical with sharp 



