MORPHOLOGY OF ACTINOMYCETES 73 



the marked shrinkage and distortion which occurs on drying. The 

 cells may be mounted in a 5 per cent glycerin solution or in Amann's 

 fluid. 



The vacuoles and "dancing bodies" of yeasts may be stained vitally 

 by suspending the cells in a dilute (1:8000) solution of neutral red. 

 Fraser ^^ has described the differential counting of living and dead 

 yeast cells suspended in solutions of neutral red, Congo red, and 

 methylene blue. Less shrinkage and distortion are observed if a 

 suspension of the cells is made in the fixing fluid and run gradually 

 through the alcohols; it should be centrifuged and resuspended at 

 each change. Finally the sediment should be imbedded in paraffin 

 and sections should be cut as thin as possible. 



The spores of yeasts may be readily observed in unstained wet 

 preparations after some experience. Beginners are likely to mistake 

 fat droplets and water vacuoles for spores. Spores may be stained 

 differentially in most cases by the use of the same procedures used 

 for staining the spores of bacteria. The following wall give beau- 

 tiful preparations. 



A dried smear is fixed in 5 per cent chromic acid for 10 minutes, stained in 

 steaming carbol fuchsin for 10 minutes or for several hours in the cold stain, 

 decolorized in 1 per cent sulphuric acid, and counterstained with Loeffler's 

 methylene blue for 2 minutes or more. Spores will be bright red, vegetative 

 cells blue. The cells within which the spores are found are frequently so 

 poorly stained as to be difficult to see. 



Morphology of Actinomycetes. For studying the morphology of 

 actinomycetes one may use the same methods that serve for the larger 

 molds, but may encounter difficulties due to their extreme minuteness. 

 The very highest magnifications must be used to obtain a clear pic- 

 ture. The slide culture method may be used to good advantage. 

 Here it is particularly important to use a medium poor in nutrients 

 in order to prevent too dense massing of the mycelium. Czapek's 

 medium is satisfactory for many species. For observing the spores 

 and sporophores the method of Drechsler^ has some advantages. 

 It consists in moistening a cover glass with a thin film of albumen. 

 This is then lightly dropped on to the surface of a sporulating colony 

 and gently lifted off again. The spore-bearing filaments will adhere 

 to the cover slip and will be pulled away from the colony, but will 

 retain their normal arrangement. They can then be fixed, stained, 

 and mounted. 



The anaerobe Actinomyces bovis can be examined by withdrawing 

 young colonies from a glucose veal infusion agar deep culture, crush- 



