[ 75- ] ! 



the help of a wash bottle), and then with a 30 % nitric acid 

 solution if the Ziehl-Neelson solution has been used, or with 

 alcohol and again with distilled water if one of the other 

 stains has been used in excess. After removing the excess 

 dye th,e cover-glass is again to be dried over the flame, and 

 then with Canada Balsam it is to be fixed on a slide. 



1.302. Counter-staining is best done by staining the 

 cover glass specimen first in the Ziehl-Neelson solution, and 

 after washing away the excess dye putting a drop of Loffler's 

 Alkaline methylene blue for a minute over the specimen 

 and then washing it out with distilled water, before the cover- 

 glass is finally dried and mounted in Canada Balsam. This 

 method of staining brings out the Tubercle bacilli very 

 prominently, these being coloured red, while pus and other 

 cells and bacteria of other kinds are coloured blue. 



1.303. Decay of food substances may be prevented in 

 various ways and this is one of the most important applica 

 tions of ^bacteriology in the field of agriculture and its allied 

 arts : 



(i) By dessication. This deprives substances of mois- 

 ture which is necessary for the growth of microbes. 

 Dessication actually kills some microbes, e.g., the cholera mi- 

 crobe. Milk, meat and fruits may be rapidly dessicated and 

 preserved in air-tight tins. The dessication of fruits and ve- 

 getables is done by the "Gnom" Evaporators (Waas patent) 

 which are sold at various prices ranging from 30 shillings to 

 30 by Messrs. L. Lumley & Co. oi America Square, 

 Minories, London, E. C, It consists of a series of trays 

 placed one above another in a vertical frame. Under- 

 neath is a hot air stove from which a current of hot air, 

 of a temperature of 120 to i8oF. passes up through 

 the series of trays. The process of drying commences 

 at the lowest of the series of trays, where the heat is the 

 greatest. By a lever arrangement the whole series of trays 

 may be lifted up admitting a tray at the bottom. Successive 



