BLOOD SERIM 47 



pares from an Irish moss (CV/r/w////rr//, 7< T m-//x rm-yms) by 

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

 filtering, the nitrate 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 



