SPECIAL PHENOMENA OF INFECTION. Ill 



by the bile or suecus entericus ; or discharged by the mucous 

 membrane of the alveoli of the lungs, the tonsils, etc. Not 

 infrequently they are discharged through suppurating wounds, 

 to which they are conveyed by the leucocytes. Many bac- 

 teria are broken up in the body and are never excreted. The 

 liver, through the bile, always excretes bacteria. The Bacillus 

 pyocyaneus, when injected into the blood-current, is excreted 

 by the functionating mammary gland. Bacteria are excreted 

 also by the sweat, and by the kidneys (tubercle and typhoid), 

 when there is a diseased condition of the renal epithelium. 

 In pulmonary diseases the bacteria are excreted largely by 

 the sputum ; in gastro- intestinal diseases, by the feces. 



Special Phenomena of Infection. 



Agglutination : Gruber found that the serum of animals 

 immune to typhoid, cholera, etc., or that of human beings 

 who had recovered from typhoid, when added to a- small 

 amount of a culture of the specific germ, caused the organism 

 to lose its motility and finally sink to the bottom of the 

 test-tube as a flocculent precipitate. Gruber called this phe- 

 nomenon agglutination, and considered it a reaction of immu- 

 nity. Widal showed later that it really represented a reac- 

 tion of the period of infection, and that the serum of 

 typhoids, at the end of the first or beginning of the second 

 week of the disease, gave the serum reaction. He concluded 

 that it represented a possible reaction of the protoplasmic 

 substance. 



The typical Widal reaction is the agglutination of the 

 typhoid bacilli when mixed with typhoid blood. When a 

 small amount of blood is added to a pure culture of typhoid 

 bacilli, the bacilli are seen to lose their motility and to gather 

 in clumps or bunches. Agglutination is not, however, char- 

 acteristic of typhoid, but is seen in many other infectious 

 diseases. If the test is performed accurately, the result is 

 absolute. The test will be described fully in the chapter on 

 Typhoid Fever. 



The agglutinating substance is contained in all normal and 

 pathologic fluids of the diseased animal, and is present through- 



