82 CLINICAL BACTERIOLOGY. 



at ordinary room-temperature. It is, therefore, best to 

 place both flask and funnel in the steam-chamber in com- 

 plete activity. Even under these circumstances the process 

 of filtering occupies several hours. The nutrient agar may, 

 further, be filtered through a warm-water funnel, consisting 

 of a copper vessel closed by a lid and containing a metallic 

 funnel into which a glass funnel can be introduced. The 

 metallic funnel is covered by a brass lid in order to pre- 

 vent evaporation. By means of a thermo-regulator, the 

 water contained in the outer filter is kept constantly at a 

 temperature of between 60 C. (140. F.) and 70 C. (158 

 F.). The prepared agar is introduced into test-tubes in 

 exactly the same way as bouillon and gelatin, and it is 

 sterilized by boiling for an hour in the steam-chamber. 

 Then it is placed in a slanting position in order to obtain 

 the largest possible surface for inoculation, or it is permitted 

 to coagulate vertically for the culture of anaerobic bacteria. 

 In the process of solidification the agar expresses a certain 

 amount of water, the so-called water of condensation. 



Gelatin and agar-agar may, like bouillon, be modified by 

 the addition of all possible substances ; thus, grape-sugar 

 two per cent., glycerin from four to six per cent., etc. Gly- 

 cerin-agar in particular plays an important part in bacteri- 

 ologic technic. It is an admirable culture-medium, suitable 

 for many pathogenic bacteria. 



For special purposes, as for the cultivation of gonococci 

 and influenza-bacilli, the preparation of blood-agar is to be 

 recommended. By means of a platinum loop several drops 

 of sterile human or pigeon's blood are smeared upon the sur- 

 face of the agar, the tubes being then placed in the thermo- 

 stat for one or two days at a temperature of 37 C. (98.6 

 F.), and the contaminated ones being rejected. Hemo- 

 globin-agar may be prepared in the same manner by smear- 

 ing a solution of hemoglobin upon the surface of the agar. 

 The solution of hemoglobin is prepared in the following 

 manner : Blood obtained with aseptic precautions is mixed 

 with an excess of physiologic salt-solution, and permitted 

 to stand in the cold for twenty-four hours. The resulting 

 precipitate of red blood-corpuscles, with water in not too 

 large amount, is introduced into a separatory funnel and a 

 like quantity of ether is added. The mixture is well, thougli 

 not too vigorously, shaken, and the dark-red, watery solu- 

 tion obtained is quickly filtered. A drop of this is smeared 



