BIRDS' EGGS 49 



tion of one part broth to three parts serum. Test-tubes 

 having been filled with the mixture and sterilised by the 

 discontinuous method, the mass is inspissated at 70° C. 



Admixture of 6 to 8 per cent, of glycerine is recom- 

 mended, and Hiippe also makes serum gelatine by adding a 

 concentrated gelatine solution, or serum agar, with a 2 per 

 cent, solution of agar, in the proportion of two to three 

 parts of either to one part of serum ; the resulting nutrient 

 media being freed from germs by fractional sterilisation. 

 These have recently been a good deal used. 



Eggs of birds. — It is well known that the white of hens' 

 eggs, when mixed with a concentrated solution of potash 

 and poured from one vessel to another, coagulates to a rather 

 firm jelly, which is known as Lieberkuhn's potash albuminate. 

 Taking advantage of this process, Tarchanoff and Koles- 

 nikoff have accordingly employed as a nxitrient medium an 

 alkaline albuminate prepared in the following way : — Hens' 

 eggs are laid without being denuded of their shells in a 5 to 

 10 per cent, solution of potash for about fourteen days. In 

 this way the white becomes firm like gelatine, probably 

 owing to a combination between the albumen and potash 

 taking place through the pores of the calcareous shell and 

 the membrane more slowly than is the case in preparing 

 Lieberkuhn's potash albuminate. If this pale yellowish 

 jelly-like mass. of albumen is cut into fine slices, and the 

 strong alkalinity got rid of by washing, a very useful nutrient 

 medium is obtained. It need hardly be said that thorough 

 attention must be paid to sterilisation, which can be done 

 in the steam steriliser. 



Plovers' egg albumen. — A convenient albuminous nutrient 

 material, which commends itself on account of its great 

 transparency and colourlessness, is the white from the eggs 

 of insessorial birds up to the time when the embryo has 

 developed its vascular area. This medium was introduced 



B 



