2 NATURAL SCIENCE [July 



against the colon bacillus possesses no agglutinating power upon the 

 typhoid bacillus, and vice versd. This test is probably of more value 

 in distinguishing between the two species than any other one test, 

 except, perhaps, the number of cilia. Yet even here the distinction 

 is not absolute. Durham has shown that there is a bacillus, the 

 B. entcritidis of Gartner (intermediate in character between the 

 typhoid bacillus and B. coli communis, though probably to be 

 regarded as a variety of the latter), which is feebly agglutinated by 

 typhoid serum, although not in such high degrees of dilution as is 

 the typhoid bacillus itself. 



There are some species of bacteria which are sharply marked 

 off : thus the tetanus bacillus is one which both morphologically 

 and in its pathogenic powers is a distinct and definite species. The 

 typhoid bacillus and B. coli communis are members of a group in 

 which the reverse is the case. The epidemiology of typhoid fever 

 can leave no doubt on the mind that B. typhosus is a distinct and 

 fixed species ; yet apart from the disease it produces, its certain 

 recognition is, as above indicated, not always so easy a matter. 

 The colon bacillus occurs in countless varieties, and has been 

 described under many different names. Its specific characters are 

 ill-marked, and it is probably a rapidly varying dominant species, 

 the characters of which are not yet fixed. 



The same may be said of the group of Streptococci. In the field 

 of pathogenesis they are as it were a ' dominant ' group, with 

 varying and ill-defined specific characters, and with equally varying 

 and ill-defined pathogenic effects. Unlike B. typhosus, which causes 

 one distinct and definite disease, it seems probable that a single 

 species of Streptococcus may give rise to suppuration, erysipelas, 

 malignant endocarditis, puerperal fever, septic peritonitis, and half 

 a dozen other diseases which clinically are distinct enough. And 

 there are probably a number of different species of Streptococci, any 

 one of which may cause a number of different diseases according to 

 its grade of virulence and seat of infection, while clinically similar 

 diseases may be due at different times to different species of 

 Streptococcus. Specificity, if such there be, is here at its very 

 vaguest. 



Compared with tetanus and diphtheria, two well-marked species 

 causing definite disease, streptococcus infection is a most complex 

 and ill-defined condition, and the task of the bacteriologist in pro- 

 viding an antistreptococcus serum is proportionately difficult. No 

 one can venture to affirm with confidence how many pathogenic 

 species of Streptococcus exist, nor whether a given case of disease is 

 due to one or other of the supposed species which are recognised. 

 Marmorek, in preparing his antistreptococcus serum, employed a 

 Streptococcus which he obtained from the fauces, and the virulence of 



