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Cultivation of Micro-organisms 



surface for the growth of the organisms. The serum thus prepared 

 should be white, but may have a reddish-gray color if many red 

 corpuscles be present. It is always opaque and cannot be melted; 

 once solid, it remains so. 



Koch devised a special apparatus for coagulating blood-serum. 

 The bottom should be covered with wet cotton, a single layer of 

 tubes placed upon it, the glass lid closed and covered with a layer 

 of felt, and the temperature elevated until coagulation occurs. The 

 repeated sterilizations may be conducted in this same apparatus, 

 or may be done equally well in a steam apparatus, the cover of which 

 is not completely closed, for if the temperature of the serum he 

 raised too rapidly it is certain to bubble, so that the desirable smooth 

 surface, upon which the culture is to be made, is ruined. 



1 



Fig. 38. — Koch's apparatus for coagulating and sterilizing blood-serum. 



Like other culture-media, blood-serum and its combinations may 

 be sterilized in the autoclave and much time thus saved. The serum 

 should, however, first be coagnlated, else bubbhng is apt to occur 

 and ruin its surface. The autoclave temperature unfortunately 

 makes the preparation very firm and hard, considerable fluid being 

 pressed out of it. 



It is said that considerable advantage is secured from the addition 

 of neutrose to blood-serum, which prevents its coagulating when 

 heated. It can then be sterilized like bouillon and can subsequently 

 be solidified, when desired, by the addition of some agar-agar. 



Fresh blood-serum can be kept on hand in the laboratory, in 

 sterile bottles, by adding an excess of chloroform. In the process 

 of coagulation and sterilization the chloroform is evaporated; the 

 serum is unchanged by its presence. 



Loffler's Blood-serum Mixture, which seems rather better for the 

 cultivation of some species than the blood-serum itself, consists of 

 T part of a beef-infusion bouillon containing i per cent, of glucose 

 and 3 parts of liquid blood-serum. After being well mixed the fluid 



