BACILLUS COLI COMMUNIS 289 



some of them are actually dissolved. This process is spoken of 

 as the immobilization, agglutination, and solution of the bacilli. 

 This serum test is known as the Gruber-Widal test. The identical 

 principle is employed in a microscopic or a macroscopic test in 

 glanders, although in this case much higher dilutions must be used 

 (see chapter on Glanders). The test and control test are frequently 

 made on a single slide with two concavities. The hanging drop with 

 water only is placed over one and the hanging drop containing the 

 dilute blood serum over the other. In making the test in the manner 

 described above, care must always be taken to have young motile 

 typhoid bacilli and to dilute the blood sufficiently. If too strong a 

 concentration of the human serum is used, a certain amount of 

 immobilization and agglutination will occur, and this may simulate a 

 positive reaction. The student must also remember that little masses 

 of blood corpuscles or fibrin are found in dried and redissolved blood ; 

 these must not be mistaken for agglutinated bacilli. In a dilution of 

 1 in 20 of the dried blood the reaction should begin to manifest 

 itself in about twenty minutes; in a dilution of 1 in 10 in less than 

 fifteen minutes, often in five minutes. When the reaction with the 

 1 in 10 dilution is doubtful lesser dilutions should always be made. 

 A positive test is not found during the very first days of the disease, 

 but about 20 per cent, of cases of typhoid give a positive reaction 

 during the first week and 90 per cent, in the fourth week. Some cases 

 of typhoid never give a positive reaction either during or after the 

 disease. The author has seen one case in which a positive reaction 

 was only obtained on a single day during the course of the disease 

 (third or fourth week), never before, never afterward. Sometimes a 

 positive reaction persists for years after the disease has run its course 

 and some permanent typhoid carriers may give a positive reaction as 

 long as they harbor bacilli. 



The Widal-Gruber test for typhoid fever has been used in hundreds 

 of thousands of cases throughout the world. If made with the neces- 

 sary precautions it is a most excellent and trustworthy test, but it 

 is not absolutely infallible on each and every application. 



The agglutination test in typhoid fever has been so fully explained 

 in all its details because it is the best known and most extensively 

 used microscopic agglutination test. Its principle and technique is 

 applicable to many microbic infections in animals, perhaps less in 

 practice but extensively in scientific laboratory work in the investi- 

 gation of problems of immunization in animal diseases. 



BACILLUS COLI COMMUNIS. 



Occurrence. The Bacillus coli communis, or Bacillus coli or colon 

 bacillus, was first found in Naples by Emmerich in the organs and 

 blood of patients who had died of Asiatic cholera. Emmerich thought 

 19 



