284 XXI. BACTERIA YEAST. 



Barclay, Pharmaceutical Chemical Manufacturers, Birmingham, 

 and G. Morton & Co., Importers and Agents, 19-21 Wilson Street, 

 Finsbury, E.G.). Besides nutrient gelatine and nutrient agar-agar 

 sterilised blood-serum is also necessary in many cases, and can be 

 obtained from them. These nutrient bases can be obtained, as 

 desired, in tubes, bulbs or flasks. Tubes are most convenient, and 

 cost about 3s. 6d. per dozen. 



Plate Cultures. For the purpose of plate cultures, the gelatine 

 is inoculated in the tube. For these purposes the tube of nutrient 

 gelatine is warmed carefully, and not too greatly, over a flame, 

 and when the gelatine has become fluid, the plug of wadding is 

 taken out. The rim of the tube is heated in the flame in order 

 to kill any germs from the air which may cling there. The gela- 

 tine is then inoculated either with a straight or a looped platinum 

 wire (previously sterilised in the flame) according to the quantity 

 of material that one wishes to transfer to the gelatine ; and with 

 this wire the material is distributed as uniformly as possible in the 

 gelatine. It is as a rule advisable not to be satisfied with this first 

 inoculation, which is almost invariably too strong, but to prepare 

 three tubes with the fluid gelatine, and after inoculating the first, 

 to take three dips from it with the platinum loop and mix care- 

 fully in the second tube, and then take three dips from this second 

 and mix with the gelatine of the third tube. Thus you have three 

 quantities of gelatine inoculated in three very different degrees. 

 The three glass plates upon which the inoculated gelatine is to 

 be poured out are placed for about a half-hour in a dry chamber at 

 a temperature of 160 C. the chamber being a box made of sheet 

 iron and closed by a dust-tight lid ; or the plates can be sterilised 

 in a flame. We wait till the plates are cool and then lay them 

 upon a larger sheet of glass which rests upon broken ice and 

 water in a glass dish. Covered with a glass bell-jar the plates 

 cool rapidly upon the ice, when the contents of the gelatine tubes, 

 which in the meantime have been made fluid and inoculated, are 

 poured out upon the plates. The plates should be 13 cm. long 

 and 8 cm. broad ; the edge should, for the space of about 1 cm., 

 remain free from gelatine. The gelatine is distributed as evenly 

 as possible over the plate by means of the rim of the tube, which 

 can with advantage be again heated before pouring the gelatine 

 out. The gelatine should set instantly. It is advisable to 

 designate the plate which received the contents of the tube first 

 inoculated wdth ; that with the first degree of dilution I ; with 



