THE INOCULATION OF ANIMALS. 91 



for. If it is invisible, pressure at the root "of the ear will 

 make it prominent. 



From the dorsal surface the hypodermatic needle is in- 

 serted at its distal extremity and the material slowly injected. 

 Care should be taken to have the needle penetrate the vein, 

 and the first few drops of injected liquid will show whether 

 it does so or not ; for if the needle is outside the vein a bulla 

 will immediately be found at the site of injection. A little 

 practice renders this method very easy. 



4. Inoculation into the lymphatics is done best with a hypo- 

 dermatic syringe and the injection is made into the testicles. 



5. Intraperitoneal inoculation requires much care and the 

 same antiseptic precautions as when opening the peritoneum 

 for a laparotomy. The skin, cleanly shaven and disinfected 

 as thoroughly as possible, is opened in the linea alba midway 

 between the sternum and pubis, through an incision, from an 

 inch and a half to two inches long and penetrating the fascia. 

 The edges of the wound being held apart, the connective 

 tissue and muscles are separated with a pair of sterilized, 

 blunt-pointed scissors. If a liquid inoculating material is 

 used, it may now be introduced with a sterile hypodermatic 

 needle into the peritoneal cavity, avoiding as much as possi- 

 ble the wounding of the intestines, which is not difficult. If 

 the material employed is solid, the peritoneum is opened with 

 scissors and the solid particle introduced into the cavity by 

 means of a sterile needle or forceps. The wound is care- 

 fully sutured and closed by a layer of collodion. 



6. Intrapleural inoculation is performed much more rarely 

 on account of the danger of wounding the lungs, and when 

 used the same precaution must be taken as for the intra- 

 peritoneal method. 



7. Inoculation into the anterior chamber of the eye is per- 

 formed occasionally to study in the living animal the changes 

 produced locally by bacteria. With a sharp-pointed bistoury 

 an incision is made in the cornea, at its sclerotic attachment 

 near the inner canthus, and the material introduced and 

 applied directly upon the iris, by a sterilized needle or by 

 means of a small forceps. 



