52 PRINCIPLES OF BACTERIOLOGY 



Serum-bouillon Media (M armorek's Media) : 



1. Human serum, 2 parts; nutrient bouillon, 1 part. 



2. Ascitic or pleuritic fluid, 1 part; nutrient bouillon, 2 parts. 



3. Horse serum, 1 to 2 parts; nutrient bouillon, 1 to 2 parts. 

 These media were first used extensively by Marmorek in cultivating 



streptococci. The ascitic fluid bouillon has been found by Williams 

 to be of great use in enriching cultures of diphtheria bacilli. It is also 

 the best medium for the growth of pneumococci, streptococci, and many 

 other pathogenic bacteria. 



Serum-water Media (Hiss' Serum Media). When diluted with 2 to 

 10 parts of water, many sera can be steamed without coagulating. 



1. Ox serum, 1 part; distilled water, 2 parts; normal sodium hydrate, 

 0.1 per cent. 



2. The same, with inulin 1 per cent, substituted for the sodium hydrate. 

 For the sterilization of undiluted fluid serum and of ascitic and 



pleuritic fluids, it is requisite that it be exposed to a temperature of 

 from 62 to 66 C. for one hour on each of six consecutive days. The 

 best apparatus for obtaining and maintaining this temperature (about 

 65 C.) is a small and well-regulated incubator or chamber surrounded 

 by a water space, into which the tubes and flasks containing serum are 

 to be put each day, and in which they are to be left for the prescribed 

 time after having been warmed to the desired temperature. 



Serum may be preserved by placing it in flasks which, after the addi- 

 tion of 5 per cent, of chloroform, are sealed. When it is to be used it is 

 filled into sterilized culture (test) tubes and sterilized by exactly the 

 same methods as are employed in sterilizing fresh serum. The chloro- 

 form, being volatile, tends to disappear at ordinary temperatures, but 

 is quickly and surely driven off at the temperatures used in sterilizing. 



Serum may be efficiently sterilized, when great care is used, by pass- 

 ing it through a well-tested Pasteur filter, under pressure. When so 

 treated the fluid is very clear and light-colored. 



Important media used for special varieties of bacteria will be noted 

 in the chapters devoted to them. 



Reaction of Culture Media. The reaction of media is a matter of 

 the greatest importance, since slight variations will often aid or inhibit 

 the growth of bacteria and also produce marked differences in the 

 microscopic and macroscopic characters of a growth. Hence it is impor- 

 tant to work with media whose reaction is accurately known, so that 

 necessary variations or uniformity can afterward be attained 



Formerly it was customary to use litmus as the indicator in neutral- 

 izing media, adding normal soda or hydrochloric acid solution until the 

 red litmus turned slightly blue, or the blue litmus just a tinge less blue. 

 This was considered the neutral point. This is still a satisfactory method 

 for those who are only going to cultivate the common pathogenic bacteria 

 for diagnostic purposes or for the development of toxin. Most parasitic 

 bacteria which grow at all on artificial culture media develop best in 

 them when they have a neutral or slightly alkaline reaction to litmus. 

 If a certain alkalinity is desired a definite number of cubic centimetres 



