BLOOD SERUM 47 



pares from an Irish moss {Carragheen, Fucus crispus) by 

 boiling 300 to 400 grms. of it with 10 litres of water, and 

 filtering, the filtrate being then evaporated and dried at 

 40° to 45° C. By the addition of 1 per cent, of this extract 

 to broth, a solid nutrient medium is obtained, which only 

 begins to liquefy at 50° C. 



Besides the modifications of nutrient broth, gelatine, 

 and agar, just mentioned, numerous other alterations and 

 additions have been proposed, the application of which is, 

 however, very limited. 



Blood serum. — The use of blood-serum as a nutrient 

 medium was introduced into the practice of bacteriology 

 by Koch. The blood from a punctured or incised wound is 

 allowed to flow into a sterilised tall glass cylinder, which is 

 then placed in an ice-tank, and allowed to stand undisturbed 

 for forty-eight hours. In this way the serum, which should 

 be of a yellow or pale red colour, separates out, and it is 

 then poured with the aid of a sterilised pipette into sterilised 

 test-tubes plugged with cotton-wool, so that there are about 

 10 ccm. of serum in each tube. The liquid serum is exposed 

 to a temperature of 56° two hours daily for a week, and freed 

 from germs by this fractional sterilisation. In order, how- 

 ever, to kill those micro-organisms also which grow at a 

 higher temperature, it is next shaken with chloroform in 

 excess, and allowed to stand for a few days, the chloroform 

 being removed by heating before use. The test-tubes are 

 then laid on a slanting surface and the serum made to set 

 at a temperature of 70° C. When solid, it should have a 

 jelly-like consistence and a yellowish colour, and should 

 adhere in its whole extent to the test-tube as a transparent 

 mass. Koch has devised a special apparatus for the inspis- 

 sation of blood serum, in which the water is carefully heated 

 for about half an hour to 68°-70° C. (fig. 23). It becomes 

 opaque at higher temperatures. Before use it must be 



