RECOGNITION OF TYPICAL B. COLI 357 



solution filtered, and 180 c.c. dilute acetic acid added. In 

 using the test, 2 c.c. of each of these solutions is added to 10 c.c. 

 of culture. If reduction of the nitrates has occurred, a rose- 

 pink colour should develop almost immediately. It is to be 

 noted that the pink colour first produced sometimes disappears 

 as it is formed or on shaking ; in such a case further portions 

 of the two reagents in equal quantities should be added. 



Agglutination Reactions of the B. coli. — When the b. coli has 

 produced a pathological condition in an animal, the serum of 

 the infected animal frequently manifests specific agglutinative 

 characters, especially towards the strain of the organism isolated 

 from the lesions. Under certain circumstances, also, the serum 

 of an animal infected by some other member of the b. coli group 

 may also agglutinate strains of this organism. This subject will 

 be treated of when we consider the differentiation of- the members 

 of the group one from another. 



Isolation of the B. coli. — In the case of abscesses or coli 

 infection of the kidney or bladder, etc. (p. 212), the isolation of 

 the organism is easily accomplished by smearing the pus or urine 

 on plates of MacConkey's lactose neutral-red agar (p. 49). 

 When the organism is present along with other bacteria, as in 

 the case of water, sewage, etc., this medium is also to be recom- 

 mended, as the bile salts present tend to inhibit the growth of 

 organisms except those belonging to the coli group. The media 

 of Conradi-Drigalski, Fawcus, and Browning (pp. 49-^51) are 

 also useful ; in these a similar inhibition is effected by certain 

 aniline dyes, picric acid, etc. All these media have their uses, 

 and it is best to select that with which the worker has had 

 most experience. The methods of the application of these 

 media and the appearances of b. coli have already been described 

 (pp. 49-51). 



The Recognition of typical B. coli. — The work on b. coli, 

 especially in relation to its occurrence in water, has revealed 

 the existence of a very large number of varieties of the organism. 

 These differ from one another in the absence of one or more 

 of the characters which may be elucidated by the application 

 of the biological methods given. Considerable difference of 

 opinion exists as to what characters are to be looked upon as 

 type characters, i.e., characters shared by the greatest number of 

 varieties isolated. In this connection it is to be noted that as 

 the b. coli was originally isolated from the human intestine, and 

 as the detection of such intestinal bacteria outside the body 

 constitutes a most important practical question, the inquiry for 

 type characters is to a certain extent limited to an attempt 



