622 



SCIENCE PROGRESS 



admitting more air to the mixing chamber. In general, anaes- 

 thesia is induced by chloroform and air at 2 per cent., and the 

 animal is kept under anaesthesia at 1 per cent, until required. 



Second step. — The anaesthetised animal is removed from the 

 bell-jar or cupboard, for the operation of tracheotomy. The 

 outlet tube of the mixing chamber is attached to the tracheal 

 tube, and anaesthesia is maintained by a mixture at between 



j 



Outlet 



Fig. 2. — The Chloroform Balance. 



i and 2 per cent., as shown by the index of the chloroform 

 balance. The chloroform-and-air is taken by the animal by 

 its ordinary respiration, or supplied to the animal by the action 

 of the pump (in which case the elastic bag and perforated 

 stop are removed from the supply tube). In either case the 

 anaesthetic vapour is under slight positive pressure — i.e. it is 

 delivered on the plenum system. 



