Chapter III —53— Morphology 



The composition of the medium is oF great importance in influ- 

 encing the manner of sporulation. Synthetic media are best for study- 

 ing this phenomenon. The process of sporulation is favored by dryness, 

 aerobic conditions, and carbohydrate nutrition. 



Cytology.— The formation of cell walls by actinomycetes has aroused 

 much speculation. Normally, growing mycelium does not show any 

 cell wall; it becomes apparent, however, when the plasma constricts and 

 breaks up into fractions. This can be seen either in old cultures or 

 during the process of sporulation of the aerial mycelium. When the 

 spores thus produced are liberated as a result of the break-up of the 

 sporophore, the empty shells become visible. The cell wall is soluble in 

 10 per cent KOH solution and in antiformin. When treated with 

 concentrated H0SO4 it is first pigmented dark and is then dissolved. 



As the great majority of the cultures do not show such septa, it has 



Fig. 12 b (see p. 52). 



generally become recognized that an actinomyces colony represents a 

 single-cell type. Drechsler (97) considered the actinomvces myce- 

 lium to be definitely septated, the hyphae being divided into short 

 sections. This phenomenon is particularly striking in cultures belong- 

 ing to the genus Nocardia, but appears only seldom among species of 

 Streptomyces. Orskov (328) also described septa in certain cultures. 

 He believed that this is the first stage in the process of the break-up of 

 the mycelium into fragments. Krassilnikov (234) considered the ob- 

 served formation of septa as merely the beginning of the fragmentation 

 process. 



In recent studies on the cytology of actinomycetes, using a more 

 refined method of staining, namely, the tannic acid-crystal violet 

 method, septa have been demonstrated (222) conclusively. They are 

 fofmed early in the vegetative mycelium. This mycelium, however, 

 although septated, never breaks up into single cells. 



