98 



NATURE 



[June 2, \\ 



continuous with the flagella where they exist. The latter 

 cannot be traced into the substance proper of .the cell, 

 a statement which the writer of this review, from his 

 own studies, especially on the bacillus of tetanus, is not 

 prepared to accept. The question whether bacteria 

 possess a nucleus is discussed at length, and the 

 author concludes that true nuclei have not been de- 

 tected, and it is improbable that they exist. All the 

 granules or structures hitherto described as nuclei, can- 

 not possibly be regarded as such ; this is clearly shown 

 by Fischer's researches on bacterial plasmolysis. In 

 studying the minute details of the bacterial cell, Prof 

 Migula rightly insists upon the absolute necessity of 

 starting from the normal living micro-organism. Ex- 

 tremely interesting is the masterly discussion of the 

 nature of the granules and vacuoles observed in the sub- 

 stance of the bacterial cell, of the origin of polar staining 

 and segmentation. In this section the subject of plasmo- 

 lysis is carefully considered. The granules so frequently 

 observed he regards as the rudimentary nucleus of the 

 bacterial cell, but he frankly admits that this view is 

 based entirely on personal opinion. One of the best 

 portions of the book is the section on the flagella, which 

 recently have been diligently studied also by Fischer, who 

 has proved that these fascinating structures are the 

 motor-organs of the mobile micro-organisms, and who 

 has attempted to classify the bacteria according to the 

 arrangement and distribution of their flagella. Prof. 

 Migula concludes that all flagellate schizophytes, ex- 

 cepting Spirochaeta and Beggiatoa, are bacteria, and that 

 different species belonging to the same family can be 

 distinguished by their flagella ; and herein all who have 

 experience of flagella staining will agree with him : the 

 number of flagella, their mode of insertion, and their 

 shape and curves — all these points must be noted. 



The growth and division of the bacterial cell is de- 

 scribed with eloquent fulness. The mode of division is a 

 generic character in the coccaceas ; it is constant, and a 

 coccus dividing in one plane by no manner of means can 

 be made to divide in two or three planes. But, further- 

 more, it is a fundamental distinctive feature between the 

 coccaceae and the other bacteria ; for the latter divide only 

 in one plane, and the division is always preceded by an 

 elongation of the cell in a direction at right angles to the 

 plane of division. Until recently it was stated that cocci 

 are as long as they are broad, and that by such measure- 

 ments they can be distinguished from the bacteria ; but 

 Prof Migula insists that we must abandon this unsatis- 

 factory distinction in favour of the one just enunciated. 

 The bacteriacece always divide at right angles to their 

 long axes, and we must therefore take exception to the 

 statements, recently made in certain quarters, that the 

 diphtheria bacillus divides parallel to its long axis. Of 

 the branching of streptococcus chains he gives two satis- 

 factory explanations : (i) occasionally in a long chain a 

 coccus becomes twisted so that its plane of division is 

 turned in a different direction ; (2) a few links in the 

 chain die, and are overgrown by the survivors. This 

 branching therefore does not signify a mycelial ancestry. 

 After division has taken place, the organisms may be 

 arranged as diplo-cocci, strepto-cocci, tetra-cocci, or as 

 sarcinae ; but it is absurd to use the terms diplo- and tetra- 

 coccus as generic ones, for many organisms belonging to 

 NO. 1492, VOL. 58] 



different genera may present all these forms. The chapter 

 on spore formation occupies fifty-three pages, and is a 

 masterly account of the subject, from which a few points 

 may be quoted. The so-called arthrospores cannot be 

 distinguished from ordinary vegetative cells, and cannot 

 therefore be regarded as spores, so that the endospore is 

 the only recognised spore. Physiological properties, 

 such as resistance against heat, desiccation, or anti- 

 septics cannot decide the nature of a spore ; the only true 

 criterion is germination, a process differing in essence 

 and in principle from ordinary vegetative proliferation by 

 division. The formation and structure of the spore are 

 described with a wealth of detail which omits no im- 

 portant fact. Broadly speaking, germination may occur 

 in three ways : ia) the membrane of the spore remains 

 unruptured, either persisting as the membrane of the 

 young bacterium, or being dissolved during the process 

 of germination ; ib) the spore-membrane is ruptured at 

 one or other pole, allowing the young bacterium to glide 

 out ; or (c) it is ruptured equatorially ; but in each case 

 there are numerous minor variations and deviations from 

 the type, depending partly upon the conditions under 

 which the germination is observed. A nucleus so far 

 has not been demonstrated in the spore, although 

 recently Hegler claimed to have done this. We must 

 fully agree with Prof. Migula when he expresses the 

 opinion that so long as we are ignorant of the natural 

 conditions of bacterial growth, we are not in a position 

 to use the faculty of spore formation for the purpose of 

 systematic classification, for many bacteria which at 

 present are described as asporogenous under more 

 natural conditions than the gelatine or agar-agar tubes 

 can supply, may actually form spores. 



Everybody will turn with interest to the chapter on 

 Pleomorphism and Variability, which opens with a historical 

 account of the views held since Nageli's time. Nageli 

 in almost unpardonable and unintelligible manner 

 ignored all morphological and physiological characters 

 of the bacteria, and became the master of the reckless 

 apostles of pleomorphism. Their creed led the philosophic 

 Buchner into the almost amusing error of proclaiming the 

 identity of the hay bacillus and the anthrax bacillus, and 

 caused the illustrious Billroth to blunder with his Cocco- 

 bacteria septica. Prof Migula insists that species must be 

 determined by identity in development and growth and 

 constancy of morphological characters ; but as yet our 

 microscopes are not perfect enough to detect the minutest 

 morphological differences, and therefore for the present, 

 in many cases, we must fall back upon biological char- 

 acters. Varieties are by no means constant, and widely 

 different form.s may constitute a species. It is impossible 

 here to discuss the question more fully ; those who take 

 an interest in such matters must consult the original. 



In the last 100 pages the biological characters of the 

 bacteria are discussed ; the different nutrient media and 

 the methods of cultivation ; the formation of pigments 

 (which are subdivided according to their solubility in 

 water and alcohol) ; the products of fermentation and of 

 metabolic activity, and the pathogenetic properties of the 

 bacteria. To the medical bacteriologist the chapter on 

 infective micro-organisms is an important one. For 

 practical purposes it is proper to distinguish between 

 pathogenetic and non-pathogenetic organisms, but this dis- 



