CUL 77 VA TION OF BA CTERTA . 133 



the culture. The serum thus prepared may be white, or 

 have a reddish-gray color if many corpuscles are pres- 

 ent, and is opaque. It cannot be melted, but once solid 

 remains so. 



Koch devised a very good apparatus (Fig. 22) for coag- 

 ulating blood-serum. The bottom should be covered 

 with cotton, a single layer of tubes placed upon it, and 

 the temperature elevated until coagulation occurs. The 

 repeated sterilizations may be conducted in this apparatus, 

 or may be done equally well in the steam apparatus, the 

 cover of which is not completely closed, for if the tem- 

 perature of the serum is raised too high it is certain to 

 bubble. 



Loffler's blood-serum mixture, which seems rather 

 better for the cultivation of some species than the blood- 

 serum itself, consists of i part of a beef-infusion bouillon 

 containing i per cent, of glucose and 3 parts of liquid 

 blood-serum. After being well mixed this is distributed 

 in tubes, and sterilized and coagulated like the blood- 

 serum itself. Most organisms grow more luxuriantly 

 upon it than upon either plain blood-serum or other 

 culture-media. Its special usefulness is for the Bacillus 

 diphtherise, which grows upon it with rapidity and with 

 quite a characteristic appearance. 



Alkaline Blood-serum. According to Lorrain Smith, 

 a very useful culture-medium can be prepared as follows: 

 To each 100 c.cm. of blood-serum add 1-1.5 c.cm. of a 10 

 per cent, solution of sodium hydrate and shake it gently. 

 Put sufficient of the mixture into each of a series of test- 

 tubes, and, laying them upon their sides, sterilize like 

 blood-serum, taking care that their contents are not 

 heated too quickly, as then bubbles are apt to form. 

 The result should be a clear, solid medium consisting 

 chiefly of alkali-albumins. It is especially useful for 

 the bacillus diphtheriae. 



Deycke's Alkali-albuminate. 1000 grams of meat are 

 macerated twenty-four hours with 1200 c.cm. of a 3 per 

 cent, solution of potassium hydrate. The clear brown fluid 



