324 AGEICXILTUKAL AND INDUSTEIAL BACTEEIOLOGY 



blood stream, causing septicemia. In fact, septicemia is 

 apparently, in many cases at least, the immediate cause of 

 death from pneumonia. When the body defenses gain the 

 upper hand, the bacteria may be eliminated and the lung 

 tissues undergo resolution. The clotted contents of the 

 alveoli undergo partial or complete autolytic digestion and 

 the material passes to the mouth or is resorbed into the 

 blood. 



Bacteriological Diagnosis. — The Diplococcus pneumonim 

 is usually recognized in sputum, when stained by Gram's 

 method, as a capsulated diplococcus, Gram-positive. Inas- 

 much as several distinct types of pneumococci have been 

 described, each capable of causing pneumonia in man and 

 perhaps in animals, it is sometimes necessary to differentiate 

 the types by the use of the agglutination test. Antisera, 

 capable of conferring immunity and having curative prop- 

 erties, have been prepared for certain types of pneumococci, 

 but not for others. It is of advantage, therefore, for a 

 physician to know what type of pneumococcus is causing the 

 disease in a particular ease. This may be ascertained by 

 securing a pure culture of the organism causing the par- 

 ticular infection and testing it against known antisera con- 

 taining agglutinins. The pneumococci are usually divided 

 into four types. Types 1, 2 and 3 are most commonly pres- 

 ent in diseases and are relatively distinct and easily recog- 

 nized. Type 4 includes forms not included in types 1, 2 

 and 3. The test is frequently carried out as follows : a bit 

 of sputum from the patient is injected intraperitoneally 

 into a mouse. At the end of a few hours the animal is 

 killed and the peritoneal cavity washed out with physio- 

 logical salt solution. The pneumococci will have multiplied 

 rapidly and by this means a milky suspension of the organ- 

 ism may be secured in relatively pure culture. Portions 

 of this suspension are then tested agafnst sera known to 

 agglutinate respectively types 1, 2 and 3. 



