GENERAL CONSIDERATIONS 7 



while the neutral red reaction is not of much assistance : other- 

 wise these tests are all valuable and satisfactory. 



Used in this way the term excretal B. colt would imply without 

 further description that all these characters were present. These 

 characters are certainly those possessed by the vast majority of 

 B. colt isolated from excreta and the term is a much more con- 

 venient one than typical since to the latter so many different 

 interpretations have been given. If any characters are negative, 

 the fact can be mentioned in brackets. Thus an organism 

 having all these attributes, except that it gives no indol reaction, 

 can be readily written excretal B. coli (indol ). 



Streptococcus group. 



The term streptococcus being only a description of a mor- 

 phological type, must obviously include a number of different 

 organisms, although Marmorek and other investigators hold that 

 all human streptococci are identical. Many different kinds of 

 streptococci have been described and much discussion has taken 

 place as to how far the described varieties are separate species 

 or mere variants of a common type. The methods in use to 

 classify streptococci are very numerous, but it cannot be said 

 that their differentiation by any method is completely satis- 

 factory nor is the basis of classification uniform for different 

 workers. 



Some investigators rely solely upon the characters most used 

 in earlier bacteriological investigations, such as morphology, 

 pigment-production, characters of the gelatine plate colonies, 

 growth in broth, milk, potato, etc. Other workers place in 

 addition to, or in substitution for, these tests, great reliance 

 upon pathogenicity, agglutination tests, or the haemolytic tests 

 introduced by Schottmuller. A further group of workers base 

 their differentiating characters in large part upon the ability of 

 streptococci to produce acid in certain sugars or alcohols. 



It cannot be said that any one series of tests is satisfactory 

 or sufficient, but speaking generally the sugar-alcohol tests, 

 together with morphology, growth in broth and milk, and patho- 

 genicity are in the writer's experience of most utility. 



