ON BACTERIOLOGY IN ITS RELATIONS TO CHE-MICAL SCIENCE. 443' 



or inability to bring abont certain chemical reactions was relied on as a 

 means of diagnosis. 



The more careful and prolonged study of individual kinds of bacteria 

 by these methods has shown, however, that the differentiation between 

 bacteria is a matter of even still greater difficulty than was hitherto sup- 

 posed. Thus during recent years there are perhaps no two bacterial, 

 forms which have been so closely and carefully studied as Eberth-Gaffky's 

 typhoid bacillus and Koch's cholera spirillum. The result of this con- 

 centrated study has been to reveal an ever-increasing number of forms, 

 so closely allied to each that their differentiation becomes more and more 

 difficult, and is based on more and more refined and artificial distinc- 

 tions. 



The extraordinary difficulty with which this branch of bacteriological 

 practice is at present attended is well illustrated by the following remarks ■ 

 of M. Metchnikoff • on Dr. Koch's last paper on the subject of the 

 diagnosis of the cholera bacillus : — 



' The characters which were formerly regarded as specific to the 

 comma bacillus, such as the form of the bacteria, their motility, the 

 manner of their growth in gelatin, suffice no more. M. Koch himself 

 describes a case of cholera in which the comma bacilli liquefied the gelatin 

 so slightly that the colonies had the form of shields (houcliers). On the 

 other hand, in the vibrio of Massowah (obtained in a cholera epidemic 

 there) we have an example of a comma bacillus which liquefies the 

 gelatin much more than the typical forms. On this account M. Koch 

 now abandons as useless the stab-cultures in gelatin. The examination 

 of drop-cultures becomes of similarly small importance, because it has 

 been shown that indisputable comma bacilli can be completely deprived 

 of motility, whilst other vibrios can be very motile. 



'The form of the vibrios is again veiy variable. Besides the vibrios 

 which are bent and thick, there are found forms which are slim and thin, 

 sometimes hardly bent at all.' 



But perhaps nothing shows the inadequacy of morphological methods 

 alone for purposes of diagnosis more conspicuously than the recent in- 

 vestigations which have been made by those newly perfected modes of 

 mordant staining devised by Loeffler, and by means of which some of 

 the finest bacterial structures — the cilia or flagella — are rendered visible 

 with a degree of precision hitherto unequalled. The observers who have 

 hoped to establish a basis of differentiation on such minute microscopic 

 distinctions as these beautiful staining methods reveal have had their 

 hopes rudely shattered by the extraordinary variability which is exhibited 

 by one and the same form in this respect. 



This variability is most strikingly exhibited by the plates of Nicolle 

 and Morax ^ of the cilia found on the cholera bacillus and its allies, as well 

 as on the typhoid bacillus and bacillus coli communis : these plates show 

 that there are as great difi'erences in the number and arrangement of the 

 cilia on cholera spirilla obtained from different sources as amongst spirilla 

 generally acknowledged to be of different kinds. Thus practically all 

 morphological distinctions, both micro- and macro-scopic, have had to be 

 abandoned as a means of final diagnosis in the case of the cholera bacillus. 



' • Kecherches sur le Cholera et les Vibrions,' Ann. de I'Inst. Pasteur, vii. (1893), 

 p. 563. 



- ' Technique de la Coloration des Gils,' Nicolle and Moiax, Ann. de I'Intt. 

 Pasteur, vii. (1893), p.5G0. 



