14 MICRO-ORGANISMS AND DISEASE. [CHAP. 



Of less common use are : 



6. Pasteur's Fluid, In 100 parts of distilled water are 

 dissolved 10 parts of pure cane-sugar, 1 part of ammonium 

 tartrate, and the ash of 1 part of yeast. 



7. Cohrfs Fluid. 100 ccm. of distilled water, 1 gramme of 

 ammonium tartrate, no sugar, and instead of the ash of yeast 

 are substituted (A. Mayer) 0'5 gramme of potassium phosphate, 

 05 gramme of crystallised magnesium sulphate, 0'05 gramme 

 of (tribasic) calcium phosphate. These two fluids are sterilised 

 in the same manner as the broth and peptone solutions. 

 Pathogenic organisms do not thrive in either of these two 

 fluids. 



B. SOLIDS. 



The solid media have the great advantage over the fluids 

 that in the former artificial cultures can be carried out more 

 easily ; as, owing to the resistance the solid basis offers to the 

 growth of the organisms, they remain more limited to the spot 

 or spots on which they are sown, and therefore can be watched 

 more easily ; besides, an accidental contamination, i.e. a growth 

 appearing at a spot at which no sowing was made, can be 

 recognised at once. These advantages are perhaps of the 

 greatest use when it is intended to grow the organisms on a 

 surface exposed to the influence of air of course protected 

 from contamination with other organisms. 



These advantages of solid media have been very minutely 

 pointed out by Koch in his researches on pathogenic bacteria. 1 



As solid media are used : 



1. Slices of Boiled Potato or Boiled White of Egg or Paste 

 (Fokker, Schroter, Colin, Wernich). Although these are of 

 great use in the study of hyphomycetes, and especially of pig- 

 ment-bacteria, they are not generally used in the case of other 

 bacteria and pathogenic organisms. The progress of the growth 

 of a particular organism sown out at a particular spot or line on 

 the surface of these substances can be easily watched with the 

 unaided eye. These substances when quite fresh are placed on 

 flat glass dishes ; these are covered with a well-fitting bell-glass, 

 the space being kept moist by a piece of moist blotting-paper 

 placed in the dish. 



2. Gelatine (Brefeld, Grawitz, Koch). This is used advan- 

 tageously as a mixture with broth, peptone, beef-extract, blood- 

 serum, or hydrocele fluid. Koch, who introduced this mixture, 

 used it for the cultivation of bacteria on solids, to be exposed 



] JUitthcilungen d. k. Gesundheitsamtes, i. 1S31. 



