I.] MILK, FIBRES, VEGETABLE ORGANISMS. 10$ 



(a.) Observe groups of small round specks, often held together 

 by a homogeneous medium. These are micrococci (fig. 60, d). 



(&.) Small elongated rod-like bodies, each moving across the field 

 in a zigzag like manner. These are bacteria (fig. 60, g). 



N.B. In all cases sketches must be made of the objects examined. 

 This holds good for this and all suwading lessons. 



17. Determine the magnifying power of the microscope. Do 

 this according to the method described at p. 1 9. 



ADDITIONAL EXERCISES. 



18. Staining of Fission Fungi or Schizomycetes. They stain readily with 

 aniline dyes, especially basic aniline colours. Scrape off a little of the coating 

 which accumulates on the surface of the molar teeth, press it between two cover- 

 glasses, so as to make cover-glass preparations. Glide the one glass off the 

 other. Place the cover-glasses, film surface downwards, in a I per cent, solu- 

 tion of methyl-violet, gentian-violet, or methylene-blue contained in a watch- 

 glass. Heat the watch glass and its contents over a gas-flame until a faint 

 cloud of vapour rises ; allow it to cool, and in 5-10 minutes or so the colora- 

 tion is complete. Remove the cover-glasses, wash them in water, and place 

 them in absolute alcohol. Remove the cover-glasses and allow them to dry in 

 the air and mount in xylol balsam. A moist cover-glass preparation from 

 absolute alcohol may be clarified with xylol. 



(.) Observe many epithelial cells coloured, but so are the organisms. 



If it is desired to ha v e only the organisms coloured, the stained cover-glasses 

 are taken direct from .he staining solution, or laved in absolute alcohol and 

 placed in a solution of iodine composed of i part iodine, 2 parts potassic iodide, 

 and 300 water, in which they are kept for a few minutes. Transfer them to 

 and wash them in absolute alcohol until nearly all colour is gone, and clarify 

 with xylol. Only the organisms are of a dark-blue tint ; the other tissues are 

 decolorised or nearly so. This is Gram's method. 



Stain bacteria from a putrefying proteid fluid, e.g., peptones 01 meat- 

 extract, in the- same way. 



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