72 APPLIED BACTEPJOLOGY 



exactly horizontal position. The sterilised glass plate is 

 placed in the glass tra.y shown in Fig. 14, and the gelatine 

 from one of the prepared tubes quickly poured on to it, 

 and distributed by means of a sterile wire over the surface. 



Fig. 14. — Plat?: C^ultuee Apparatus. 



care being taken not to bring the gelatine too near the 

 edge. The glass cover is then lowered, and other plates 

 can then be prepared in the same way by placing them on 

 a metal or glass rack over the first plate. 



Petri's Dishes. — The use of these has some advantages 

 over the plate method of Koch. The dishes are from 10 to 

 20 centimetres wide and about 1".5 or 2 centimetres deep, 



=^^*^ 



Fig. 1.5. — Petri Dourle Dish. 



""""'"'" "^'"^'"" """"Ts of the same form as the 



lishes can be safely carried 



v'elling apparatus ; moreover, 



and counted if desired with- 



consequently, without the 



exposure to contamination to which Koch's form of plate 



is liable. Petri's double dishes are made both in the round 



and square form. 



Esmareh's Eoll Cultures. — A useful modification of Koch's 

 method is that of A'on Esmarch. Instead of pouring the 



