360 EXPERIMENTAL INOCULATION OF ANIMALS 



12. When cool wash the sac in sterile water, then 

 transfer to a tube of nutrient broth and incubate 

 over night to determine its impermeability to bacteria. 



13. If the broth outside the sac remains sterile, 

 insert the sac in the peritoneal cavity of the experi- 

 mental animal. 



5. Intracranial. (Anesthetic, A. C. E.) 

 Trephines and Surgical Engine. The most useful 

 instrument for intracranial operations upon animals 

 is the small nasal trephine (Curtis) having a tooth cut- 



FIG. 1 86. Guarded trephine. 



ting circle of 7 mm. The addition of an adjustable 

 collar guard secured by a screw prevents acciden- 

 tal laceration of the dura mater or brain substance 1 

 (Fig. 1 8 6) . This size is suitable for monkeys, dogs, cats 

 and large rabbits. Other smaller sizes which will be 

 found useful for guinea pigs and other small animals 

 cut circles of 6 and 4 mm. ; for very small animals 

 young guinea pigs and rats a small dental drill or 

 screw will make a sufficiently large hole to admit the 

 syringe needle. The trephine can be set in ordinary 

 metal handles and rotated by hand, but a surgical 

 engine of some kind is much preferable on the score 

 of rapidity and safety to the animal. The Guy's elec- 

 trical Dental engine 2 (Fig. 187) which can be connected 

 to a lamp socket or wall plug, and is operated by a foot 

 switch, although inexpensive is eminently satisfactory. 



NOTE. A fine dental drill attached to the dental engine renders 

 the manufacture of aluminium handles needles (see page 71) 

 quite an easy matter. 



1 This modification is made for the author by Messrs. Down Bros., St. 

 Thomas's Street, London, S. E. 



2 Manufactured by Messrs. Francis Lepper, 56, Great Marlborough 

 Street, London, W. 



