344 Veranus Alva Moore 



(including etiological) properties, is one which, as j^et, has no 

 clearlj^ defined and uniformly accepted answer. Messea's 

 classification of motile bacteria is based on morphological 

 characters only, and it recognizes genera, but not species. 

 lyUksch goes still further and points out a specific difference 

 in the number of fiagella of the typhoid and colon bacilli, two 

 well recognized species of one genus. On the other hand, the 

 more extended investigations of the biological properties of 

 bacteria are continually bringing forth new facts, and reveal- 

 ing variations in the properties of these organisms which are 

 not explained by corresponding differences in their morpholo- 

 gy. There are bacteria which possess marked difference in 

 their biological manifestations which resemble each other so 

 closely in their structure that, with our present knowledge, 

 their differentiation by purely morphological characters, is 

 practically impossible. In the group of bacteria which 

 includes Bacillus cholera suis, Bacillus coli com^nunis, and 

 Bacillus typhi abdorninalis we have an excellent illustration 

 of this fact. These species resemble each other very closelj' 

 morphologically but they are readily differentiated by means 

 of their biological and etiological properties. In this group, 

 therefore, is found a most rigid test for the differential value 

 of the fiagella. 



It may be assserted that these bacteria do not belong to the 

 same group, and while in a narrow sense (considering their 

 more characteristic physiological manifestations only) it may 

 be true, yet morphologically they are small, motile bacteria 

 belonging to the Peritricha (Messea) and, in certain other re- 

 spects, they are closely enough related to one another to be 

 enrolled in the same genus, while their physiological and eti- 

 ological properties mark their specific differences. In order 

 that the differential importance of the biological and etiolog- 

 ical properties of these bacteria may not be overlooked in the 

 subsequent consideration of the specific character of their 

 fiagella, a brief summary of the more important of these prop- 

 erties for each of the germs in question, is appended : 



(a). Bacillus cholera suis is a small actively motile genu which 

 is found in the organs of swine suffering from hog cholera. It 



