306 Microorganisms (chap. 20) 



forms (must grow in air). Burrows (1954) uses the name Actinomyces 

 for the pathogenic actinomycetes. 



The fungi proper (Eumycetes) also form hyphae and mycelia. They 

 give off two types of spores, sexual spores produced by the fusion of 

 two cells and asexual spores formed by differentiation of the cells 

 of the spore-bearing hyphae biu without fusion. The so-called Fungi 

 Imperfecti (part of the Eumycetes) form only asexual spores. These 

 spores in some forms may be produced by the segmentation of the tips 

 of the hyphae and are known as conidia {Penicillium). 



Open or draining lesions are difficult to examine for fungi because 

 of heavy bacterial contamination, but dermatophytes are easily demon- 

 strated. Scrapings from horny layers or nail plate or hair can be moinited 

 in 10-20% hot sodium hydroxide. This dissolves or makes transparant 

 the tissue elements and then the preparation can be examined as a wet 

 mount. Fungi in tissue sections are readily stained. 



Yeast and Yeast-like Fungi. These are described as unicellular and 

 nucleated. Some yeasts reproduce by budding and others by fission. 

 Some can produce mycelium. Only a few are pathogenic, causing torula 

 meningitis, European blastomycosis, and superficial infections of skin 

 and mucus membranes. 



Viruses. The viruses are microorganisms too small to be visible mider 

 the microscope and are capable of passing through filters. Viruses are 

 responsible for many diseases, including yellow fever, poxes, poliomye- 

 litis, influenza, measles, mumps, shingles, rabies, colds, infectious hepa- 

 titis, infectious mononucleosis, trachoma, psittacosis, and foot-and-mouth 

 disease. In tissue sections and smears, viruses are characterized by ele- 

 mentary and inclusion bodies. Elementary bodies are infectious parti- 

 cles, and inclusion bodies are composed of numerous elementary bodies. 

 Both types of bodies vary in size and appearance; some are located in 

 the cytoplasm of infected cells (rabies, psittacosis, trachoma) and some 

 are intranuclear (poliomyelitis). Special staining methods can demon- 

 strate them effectively. {Reference: Burrows, 1954) 



Animal Parasites. Protozoan, helminth, and arthropod infections: 

 see Chapter 23. 



Bacteria Staining 



Gram Staining 



When a gram staining procedure has been applied, a gram-positive 

 cell or organism retains a particular primary dye. This process includes 



