SERUM MEDIA. 45 



canula and india-rubber tube, tbe former being inserted in the 

 blood-vessel. The serum obtained under such circumstances 

 must be incubated before use, to make sure that it is sterile. 



Ldffler's Blood Serum. — This is the best medium for the 

 growth of the B. diphtherias and may be used for other organisms. 

 It has the following composition. Three parts of calf's or lamb's 

 blood serum are mixed with one part ordinary neutral peptone 

 bouillon made from veal with i per cent of grape sugar added to 

 it. Though this is the original formula it can be made from ox 

 or sheep serum and 'beef bouillon without its qualities being 

 markedly impaired. Sterilise by method B (4) as above (p. 32). 

 Or we may adopt the more* rapid method in bringing about 

 coagulation at a high temperature, by placing the tubes as before 

 in the inspissator and slowly raising the water in the jacket of 

 the apparatus to the boiling-point and then turning out the gas. 

 The serum will be found to be firmly coagulated and free from 

 bubbles, if the precaution were taken to keep the tubes of 

 serum free from contact with the metal bottom or sides of the 

 inspissator by means of thin wooden slats properly adjusted. 

 The medium must then be sterilised on three successive days in 

 the Koch or Arnold steriliser. 



Alkaline Blood Serum (Lorrain Smith's Method). — To each 

 100 c.c. of the serum obtained as before, add i to 1.5 c.c. of a 

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

 Put sufficient of the mixture into each af a series of test-tubes, 

 and laying them on their sides, sterilise by method B (2). If the 

 process of sterilisation be carried out too quickly, bubbles of gas 

 are apt to form before the serum is solid, and these interfere 

 with the usefulness of the medium. Dr. Smith informs us that 

 this can be obviated if the serum be solidified high up in the 

 Koch's steriliser, in which the water is allowed only to simmer. 

 In this case sterilisation ought to go on for one and a half hours. 

 A clear solid medium (consisting practically of alkali-albumin) is 

 thus obtained, and he has found it of value for the growth of the 

 orgahisms for which Koch's serum is used, and especially for 

 the growth of the B. diphtherias. Its great advantage is that 

 aseptic precautions in obtaining blood from the animal are not 

 necessary, and it is easily sterilised. 



Marmorek's Serum Media. — There has always been a diffi- 

 culty in maintaining the virulence of cultures of the pyogenic 



