EXAMINATION OF MATERIAL FROM PATIENTS 175 



fluids are collected for bacteriological examination, such as spinal fluid, 

 paracentesis fluid, or pleural exudate, it is convenient to have them taken 

 directly into sterilized centrifuge tubes, since it is often necessary to 

 concentrate cellular elements by centrifugalization. By immediate col- 

 lection in these tubes, the danger of contamination is avoided. 



Examination of Exudates. Pus. Pus should first be examined 

 morphologically by some simple stain, such as gentian-violet, and by 

 the Gram stain. It is convenient, also, to stain a specimen by Jenner's 

 stain, in order to show clearly the relation of bacteria to the cells. 

 Such morphological examination not only furnishes a guide to future 

 manipulation, but supplies a control for the results obtained by cultural 

 methods. Specimens of the pus are then transferred to the proper 

 media, and pour-plates made or streaks made upon the surface of 

 previously prepared agar or serum-agar plates. 



A guide to the choice of media is often found in the result of the 

 morphological examination. In most cases, it is well also to make 

 anaerobic cultures by some simpler method. (See page 148 et seq.) 



The colonies which develop upon the plates should be studied under the 

 microscope, and specimens from the colonies transferred to cover-glasses 

 and slides for morphological examination and to the various media for 

 further growth and identification. Animal inoculation and agglutination 

 tests must often also be resorted to. A knowledge of the source of the 

 material may furnish considerable aid in making a bacteriological diag- 

 nosis, though great caution in depending upon such aid is recommended. 

 In the examination of peritoneal, pericardial, or pleural exudates it is 

 often advantageous to use the sediment obtained by centrifugalization. 

 A differential count of the cells present may be of aid in confirming the 

 bacteriological findings. Morphological examination and cultural exam- 

 ination are made as in the case of pus. Specimens should also in these 

 cases be stained for tubercle bacilli. Whenever morphological exami- 

 nations 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 inocu- 

 lation. Guinea-pigs should be inoculated intraperitoneally from speci- 

 mens 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 



