II. J PREPARATION OF CULTURE MATERIAL. 21 



6. Urine is neutralised and sterilised by boiling for 20 to 

 30 minutes like broth. 



7. Milk (ordinary) is sterilised by gentle and careful 

 boiling for 20 to 30 minutes. 



Of less common use are : 



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

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

 tartrate, and the ash of i part of yeast. 



9. Cohris Fluid. 100 ccm. of distilled water, i gramme 

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

 yeast are substituted (A. Mayer) 0-5 gramme of potassium 

 phosphate, 0*5 gramme of crystallised magnesium sulphate, 

 0*05 gramme ot (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 contami- 

 nation, 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 



