CULTIVATION OF BACTERIA 



51 



(b) Heated Blood Media. The clot containing the red cells, after the 

 separation of the serum, is broken up and added to bouillon and heated 

 to 80 to 90 C. This makes a muddy fluid which is fitted only for 

 the development of bacteria where no observation of their growth is 

 required. 



BLOOD-SERUM MEDIA. ASCITIC OR PLEURITIC FLUID. Blood serum 

 may be sterilized by fractional sterilization and remain fluid, or it may 

 be rendered solid by the degree of heat used in sterilizing. The blood 

 is obtained from an ox, horse, sheep, dog, or rabbit and collected into 

 jars, flasks, or tubes. When it is to be used in a fluid state it should be 

 drawn in an aseptic manner into a flask from a vein by means of a 

 sterile cannula and rubber tube. When it is to be solidified, less care is 

 necessary. It is here sufficient to catch the blood from the cut artery 

 or vein into sterile jars or tubes. To facilitate clotting it is well to have 

 in the jar or tube something for the clot to contract around. 



Loeffler's Blood Serum. Three parts of a calf's or sheep's blood is 

 mixed with one part of neutral peptone bouillon containing 1 per cent, 

 of glucose. The serum mixture is run into tubes, which are plugged and 

 then placed in a slanting position in the serum inspissator. 



Serum may be solidified and still remain translucent at a temperature 

 of 76 C., but when heated to a higher degree a more definite coagula- 

 tion takes place, and the medium becomes opaque. Care must be 

 taken in coagulating blood serum at the higher temperature to run the 

 temperature up slowly, and not to heat above 95 C. until the serum 

 has firmly coagulated; for, unless these precautions are taken, ebullition 

 is likely to occur, which will lead to the formation of bubbles and an 

 unevenness of the surface upon which growth is to be obtained and 

 studied. Serum may be solidified 

 at the temperature mentioned in an 

 incubator, water-oven, or even in 

 an Arnold sterilizer with the top 

 covered by a cloth instead of the 

 usual lid, and when coagulated 

 firmly (90 C.) the tubes and their 

 contents may, on the following day, 

 be sterilized in streaming steam 

 at 100 C. without danger of the 

 subsequent formation of bubbles. 

 Koch's serum coagulator (Fig. 22) 

 is, however, the most convenient 



apparatus. Some bacteriologists prepare the tubes of solidified serum 

 in the autoclave, gradually increasing the temperature to 110 C. This 

 is a very rapid and convenient method. It has seemed to us, however, 

 that the high temperature injured the medium somewhat. 



Alkaline Blood Serum. To each 100 c.c. of blood serum add 1 to 1.5 

 c.c. of a 10 per cent, solution of sodium hydrate. Treat as Loeffler's 

 serum. This will give a solid, clear medium consisting chiefly of alkali 

 albumin. 



