102 



OPERATIVE TECHNIQUE. 



fifteen to thirty seconds may be allowed to elapse. Speciall}' thick 

 tissues may be divided in two portions, the centre being perforated, 

 and the chain applied alternately to either side. 



The Galvanic or Thermo-cautery.— In the galvanic cautery 

 a loop of platinum wire is passed around the tissue to be divided, 

 and after being raised to a bright red heat by the passage of an 

 electric current, is graduall}- drawn tight. On account of its com- 

 plications and expense, however, this instrument is ver}' seldom 

 used in veterinar}' surgery, especiall}^ as Paquelin's thermo-cautery 

 (Figs. 114, 115) renders almost equall}- good service and is much cheaper. 

 The thermo-cautery consists of a hollow platinum terminal which 

 ma}' be of varying shape. After being heated in a spirit flame it is kept 

 at a bright red heat by injecting a mixture of ether or benzine vapour 

 and air into the head. Tissues divided by this instrument bleed ver}^ 

 little, though the scab produced by the cautery must have a certain thick- 

 ness, to attain w^hich the division must be made deliberately. The 

 wounds produced heal comparatively slowly. 



Puncture. — A puncture is an incision of considerable depth but 

 of comparatively small diameter. Puncture to permit fluids or gases 



P'lc;. I2T, 



Fig. 121. 



Fig. 122 



to escape from cavities, like the thorax, abdomen, or bowel, is termed 

 paracentesis. To prevent the entrance of air into deeper seated tissues 

 or into the cavity to be opened, the skin is often drawn to one side 

 before operation, so that returning afterwards to its ordinary- position it 

 closes the deeper opening. Subcutaneous puncture ma}- also be prac- 

 tised by first introducing the perforating instrument horizontally a 

 short distance under the skin, and, after altering its direction, making 

 the desired puncture ; the walls of the opening immediately collapse on 

 the removal of the instrument. 



An ordinary pointed knife, bistour}', scalpel or lancet may be used 

 for puncturing. Either of the former is held like a pen, the thumb 



