Chapter III _ 67 — Morjjhology 



28 °C. or at higher temperatures results in loss of activity, the rate of 

 loss being proportional to the temperature (Table 7). 



Constancy of actinomyces tyfes.— Each one of the four genera of 

 actinomycetes has clearly defined morphological characters. Although 

 there is a certain amount of overlapping between the species within the 

 different genera, notably between the species of Actinomyces and of 

 Nocardia, or between Nocardia and Stre'ptomyces, the combined 

 morphological and cultural properties well characterize each genus. 

 Very often a species of Streponiyces may lose, by selection or by 

 mutation or natural variation, the property of forming aerial mycelium; 

 it may then appear to become a t)q5ical Nocardia. This was shown to 

 hold true, for example, of the streptomycin-producing strain of S. 

 griseus. When such a change occurs, it is accompanied by a change 

 in the physiology of the organism. Usually, however, the culture re- 

 verts to its original form under proper methods of cultivation. 



Table 7: Stability of phage in aqueous suspension upon storage at several temperatures (355): — 

 Phage particles X 10^ per ml, after storage* 



Temperature — 

 OF STORAGE, 3 days 12 days 29 days 



°C. 



6 44 - 60 



28 31 20 0.00005 



37 37 15 0.0000009 



56.5 18 0.001 



* At start all preparations contained 36 X 10' particles of phage per ml. 



This emphasizes the fact that there is a marked interrelation be- 

 tween the morphological and physiological properties of an organism. 

 Ample evidence of this has been established for the rough and the 

 smooth strains of bacteria. Apparendy such interdependence, though 

 of a somewhat different kind, exists also among actinomycetes. 



The four genera of the actinomycetes have been shown to possess 

 constant morphological properties, with a limited overlapping of the dif- 

 ferent genera. These properties may be summarized as follows: 



The genus Actinomyces comprises the anaerobic pathogenic forms. 

 It is characterized by a gram-positive, non-acid-fast, branching vegeta- 

 tive mycelium. No aerial hyphae are formed. The mycelium tends 

 to break up into bacillary forms. 



The genus Nocardia is characterized by the formation of an un- 

 divided substrate mycelium in the early stages of development. Aerial 

 mycelium may be formed among certain members of the group, but it 

 is usually indistinguishable from the substrate mycelium. The non- 

 septated hyphae of both the substrate and the aerial mycelium break 



