THE DETECTION OF BACTERIAL PATHOGENICITY 233 



Intranasal. In most instances the material is dropped into the nostrils 

 and the animal is allowed to insufflate or the material is sprayed onto the 

 membranes of the nose and throat. Light anesthesia is generally neces- 

 sary and desirable to quiet the animal before intranasal inoculation is 

 attempted. The operator should take care that he himself does not 

 inhale any of the material, and it is absolutely essential that intranasal 

 inoculation never be performed unless the operator is suitably masked. 

 In certain instances it may be desirable to use a small chamber, such as a 

 metal mouse box covered with a glass plate, in which the animal can be 

 exposed to an infective aerosol. The latter may be introduced through 

 an opening in the side of the chamber with an atomizer or nebulizer. 

 The aerosol chamber minimizes the exposure to the operator. However, 

 it is essential that care be taken to prevent leakage from the system, and 

 the animals should be removed from the chamber with proper precautions. 



Intratracheal. The material may be introduced into the trachea 

 through a tube placed in the larynx or by means of a syringe through the 

 side of the neck. In the latter method the skin may be incised after 

 shaving and sterilization. 



Ophthalmic. Material is dropped into one eye, the other left un- 

 treated, as a control. It may also be inoculated upon the scarified 

 conjunctiva. 



Intracerebral. The method of injection will vary with the different 

 species of animals and the desired location for the inoculum. In most 

 instances it is deposited into one of the frontal lobes. Care should be 

 taken not to inject on the midline of the skull, since a large sinus lies 

 below and fatal hemorrhage may result. A trephine or punch is neces- 

 sary to open a hole in the case of guinea pigs and larger animals which 

 have relatively thick skulls. A trephine is not necessary in the case of 

 mice, hamsters, or smaller rats. Do not use a volume which is great 

 enough to cause pressure. For larger animals one can inoculate 0.5- 

 1.0 ml; for medium-sized animals, as guinea pigs, 0.1-0.25 ml; and for 

 small animals, as mice and hamsters, 0.03-0.05 ml. 



Intracardial. Initial attempts at intracardial injection may fail, but 

 numerous attempts are inadvisable because the animal usually develops 

 a hemothorax from punctures of the heart. This method is most easily 

 performed if the animal is anesthetized, the skin disinfected, and then the 

 area of maximum beat of the apex of the heart is palpated by means of 

 the forefinger. When the heart has been located, a sharp needle (the 

 size depending upon the animal) should be inserted between the ribs and 

 pushed in the direction of maximum palpation. One should then be able 

 to feel the heartbeat pulsating against needle and syringe. When this is 

 established, the needle can be readily plunged into the heart, but care 

 should be taken not to push too deeply or it will pass through the chamber 



