Chapter II — 33 — Important Types 



Many strains invert saccharose. Some strains reduce nitrate to nitrite. Most 

 strains decompose cellulose. Proteolytic action seems stronger in this than in the 

 other species of this genus. Optimum temperature for growth, 30-35°C. Thermal 

 death point of mycelium, 70°C. in 2 to 5 minutes. Spores resist 80°C. for 1 to 

 5 minutes. 



Habitat: Soil, lake mud, and other substrates. 



This genus could be subdivided on the basis of the relations of the 

 organisms to temperature, since it includes a number of thermophilic 

 forms which grow readily at 55°-65°C., mesophilic forms having their 

 optimum temperature at 30°C., and organisms growing at low tempera- 

 ture in lakes. Each of these can be divided into diree groups, based on 

 the structure of the spore-bearing hyphae. Among the thermophilic 

 forms, only representatives of the first group have so far been isolated in 

 pure culture, although the existence of the other two groups has defi- 

 nitely been demonstrated in microscopic preparations. These are: 



Group 1. Simple spore-bearing hyphae. 

 Group 2. Branching spore-bearing hyphae. 

 Group 3. Spore-bearing hyphae in clusters. 



Description of Several Important Actinomycetes:— In view of the 

 great economic importance of some of the actinomycetes, several species 

 with unusual physiological properties or of great practical value are 

 described in detail here. 



Actinomyces hovis Harz. 



A. hovis is an anaerobic pathogen. It's most recent description, 

 under the name of A. israeli, is given by Rosebury (367). This work 

 served as a basis for the following summary. 



A. hovis is a gram-positive, branching, filamentous organism, non- 

 acid-fast, and not producing spores. The hyphae are usually less than 

 lit. in diameter. In tissue sections made from the lesions of actinomy- 

 cosis, the organism appears in the form of compact granules or colonies 

 which are often visible to the naked eye. The granules are circular or 

 irregular in outline, or may comprise several colonies of different size 

 and shape which have grown together. Each granule consists of a 

 dense mass which stains irregularly in hematoxylin-eosin preparations 

 biit takes the violet dye in sections stained by Gram's method. The 

 ends of individual filaments may be seen around the periphery of the 

 granule, or part of the periphery may be composed of the radially ar- 

 ranged hyaline clubs. These can be stained with eosin. They are 

 several times wider than the filaments, which can sometimes be traced 

 within the structure of the club. 



In exudates from actinomycosis, certain sulfur granules make their 

 appearance. These are irregularly spherical masses, varying in diame- 



