822 PATHOGENIC MICROORGANISMS 



2. Do not make packages too small, as small packages are more likely 

 to be lost in transit, or overlooked. 



3. Each package should be marked as follows: 



Notice 



This package contains perishable specimens 



for bacteriological examination 



Please Expedite 



Careful autopsy must of course be made on all cases, animal or 

 man, and the lesions studied. The lesions in rats have been fully 

 described in another section. Cultures are taken on agar and smears 

 taken from buboes or sputum, stained by Loeffler's methylene-blue, 

 the bipolar appearance and degeneration forms of the organisms 

 looked for. Cultural diagnosis is then made by the appearance 

 of the growing organisms, and their colonies, the staining properties, 

 appearance on salt agar, agglutination in immune sera, and, above 

 all, inoculation of rats and guinea-pigs with observation of the 

 characteristic lesions in these animals. 



Since the examination of rats for plague is an important phase 

 of the study of epidemics, it may be well to review the typical lesions 

 in these animals as described by an experienced American student 

 of plague, George W. McCoy. 24 McCoy, agreeing with the Indian 

 Plague Commission, states that the naked eye is superior to the 

 microscopical examination. There is engorgement of the subcutane- 

 ous vessels and a pink coloration of the muscles. The bubo when 

 present is sufficient for diagnosis. Marked injection surrounds it 

 and sometimes there is hemorrhagic infiltration. The gland itself 

 is firm but usually caseous or occasionally hemorrhagic. In the liver 

 there is apparent fatty change, but this is due to necrosis. Pin-point 

 spots give it a stippled appearance as though it had been dusted 

 with pepper. Pleural effusion is an important sign. The spleen 

 is large, friable, and often presents pin-point granules on the surface. 

 One or two per cent of rats may present no gross lesions. Cultures 

 should of course be made. The method of examination consists in 

 immersing the rat in any convenient antiseptic to kill fleas and other 

 ectoparasites. The rats ar*e nailed by their feet to a shingle and 

 the skin is reflected from the whole front of the body and neck, 

 so as to expose the cervical, axillary, and inguinal regions. The 

 thoracic and abdominal cavities are then opened and examined. 



24 McCoy, Jour, of Inf. Dis., vi, 1909 ; George W. McCoy, Public Health Beports, 

 July, 1912. 



