208 BIOLOGY AND TECHNIQUE 



knowledge of the source of the material may furnish considerable 

 aid in making a bacteriological diagnosis, though great caution in 

 depending upon such aid is recommended. 



If the morphological examination shows Gram-positive micro- 

 cocci, as in staphylococcus boils, any ordinary properly made agar 

 will suffice. 



If streptococci are present in the Gram stain, it will be useful 

 to employ blood agar plates without glucose. 



When the pus is gonorrheal, ascitic agar plates with glucose 

 should be used, and the pus transferred directly from the patient 

 to the plate and incubated before it chills. In the case of pus from 

 abrasions of the skin, furuncles or boils that arouse any suspicion 

 of anthrax a careful search for Gram-positive bacilli should be made 

 with the Gram stain, and the characteristic colonies looked for on 

 ordinary agar plates. 



When plentiful leucocytes are present and the pus shows no 

 organisms in smear, this should not discourage culture since it is 

 not unusual to obtain colonies on culture when nothing can be 

 found by smear. 



In the examination of peritoneal, pericardial, or pleural exudates 

 it is often advantageous to use the sediment obtained by centrifugaliza- 

 tion. A differential count of the cells present may be of aid in confirm- 

 ing the bacteriological findings. Morphological examination and cul- 

 tural examination are made as in the case of pus. Specimens should 

 also in these cases be stained for tubercle bacilli. Whenever mor- 

 phological examinations of such fluids are negative, no bacteria 

 being found, and especially when among the cellular elements the 

 lymphocytes preponderate, the search for tubercle bacilli should be 

 continued by means of animal inoculation. Guinea-pigs should be 

 inoculated intraperitoneally with specimens of the fluid. The 

 animals will usually die within six to eight weeks, but can be killed 

 and examined at the end of about six weeks if they remain alive. 

 The chances for a positive result are considerably increased if the 

 fluid is set away in the ice-chest until a clot has formed and the 

 animals are inoculated with the material from the broken-up clot. 



Spinal Fluid. Normal spinal fluid is a clear, colorless fluid which 

 contains not more than ten to twelve cells per cubic millimeter. 

 Anything above this should be regarded as suspicious. When clear 

 spinal fluid is brought to the laboratory it is always well to shake 

 up the specimen and do a direct count. 



