THE STUDY OF THE GROWTH OF BACTERIA 105 



BLOOD SERUM. 



The blood of a dog drawn under strictly aseptic precautions 

 from a vein of an anesthetized dog is collected in a sterile jar and 

 after the serum has separated, it is run into tubes by sterile pipettes 

 and simply coagulated by heat. Sterilization is not necessary, and 

 is harmful for the growth of the tubercle bacilli, because salts are 

 formed which interfere with the growth of the bacteria. 



LOFFLER'S BLOOD SERUM MIXTURE. 



Blood serum of an ox or a horse is employed, mixed with bouillon 

 containing i percent of grape sugar. 



Seventy-five percent of blood serum is mixed with 25 percent 

 bouillon. This is run into sterilized tubes and the latter are placed 

 in a blood serum coagulator and coagulated in a sloping position 

 at a temperature of 65 C. or thereabouts. 



After they are coagulated they are sterilized by heating an hour 

 each day at 65 C. five successive days, or at 95 C. for an hour on 

 three successive days. After sterilization the tubes should be sealed 

 carefully. 



Egg are employed as culture media. The yolks and whites of a 

 number of eggs are shaken together in a flask and then strained 

 through a towel to remove the froth. The mixture is then run 

 into tubes and coagulated and sterilized like blood serum. On 

 this mixture the tubercle bacillus grows very well. 



These are the common culture media used in laboratories. For 

 a more technical description of the manufacture of these and other 

 media, the student is referred to books devoted to laboratory technic. 



Litmus tincture is made by adding a large handful of litmus cubes 

 to a pint of water and boiling down to one-fourth its volume. This 

 is then filtered through paper and stored after sterilization. 



The Study of the Growth of Bacteria. Cultures. 



Bacteria growing in groups on culture media are spoken of as 

 colonies. Aerobic bacteria may be made to grow on culture media 



