74 



NATURE 



[May 28, 189T 



painting the skin immediately outside the erysipelatous 

 area with some counter-irritant. The authors have 

 studied the rationale of this treatment, and conclude 

 that the irritant brings about the formation of a 

 zone of inflammation, with dilatation of the vessels 

 and diapedesis of the white corpuscles, which now, 

 by destroying the micrococci, act as a barrier to the 

 further progress of the disease. With the malignant 

 pustule produced by the inoculation of the anthrax bacilli, 

 similar counter-irritation was effectual in only three out 

 of thirty cases — that is to say, with the more active virus 

 the stimulus applied was not sufficient to produce an 

 effectual barrier. J. George Adami. 



THE CHEMICAL AND BACTERIOLOGICAL 



EXAMINATION OF POTABLE WATERS. 

 Exavien Quimico y Bacteriologico de las Aquas Potables. 

 Por A. E. Salazar y C. Newman, con uno capitulo 

 del Dr. Rafael BJanchard sobre " Los Animales Para- 

 sites introducidos por el Aqua en el Organismo." 

 (London : Burns and Gates, 1890.) 

 A PECULIAR interest attaches to this work at the 

 -^"^ present moment in consequence of the sad political 

 events now going on in the country from which it has 

 emanated ; for, whilst almost each successive day brings 

 news of the sacrifice of human life in one of the fiercest 

 and most sanguinary civil contests of recent years, the 

 object of this book is to show how the latest results of 

 scientific research may be applied to combating on the 

 same soil some of the ills which flesh is heir to. The 

 publication of this treatise for Chilian students affords the 

 strongest evidence of the rapidity with which scientific 

 knowledge traverses the globe at the present day, and it 

 must be a source of great satisfaction to all interested in 

 the dissemination of the principles of hygiene that there 

 should be a demand for a work of such an advanced 

 character in a country so remote from what we are wont 

 to regard as the centres of civilization. 



The scope of this work is more comprehensive than 

 that of perhaps any similar one in our own language ; 

 English treatises on water analysis being in general only 

 short manuals giving instructions for the execution of 

 analytical methods devised by their authors, who usually 

 dismiss the rival methods of others with a few words, 

 often not of a very complimentary kind. The pages 

 under review, however, not only give an interesting ac- 

 count of the various methods employed by water-analysts, 

 but subject their several claims to a fair and impartial 

 criticism, whilst detailed information is supplied for carry- 

 ing out those methods which the authors regard as, on 

 the whole, the most serviceable. Again, a most exhaustive 

 account is given of the bacteriological examination of 

 water, including precise instructions for the cultivation of 

 micro-organisms, the preparation of nutritive media, the 

 sterilization of apparatus, the use of the microscope, and 

 the performance of inoculation experiments on animals. 

 But even this ample programme was inadequate for the 

 ambition of the authors, who have associated with them- 

 selves a third colleague, who contributes a bulky ap- 

 pendix on " the animal parasites gaining access to the 

 organism through water." The work is not only profusely 

 illustrated with cuts, but contains also a number of ori- 

 NO. I 126, VOL. 44] 



ginal photographs representing both the microscopic and 

 macroscopic appearance of some bacteria. Indeed, the 

 bacteriological part is the real centre of gravity of the 

 work. A decade will soon have elapsed since the bac- 

 teriological examination of waters began to attract much 

 attention in consequence of the ingenious method o 

 gelatin-plate cultivation devised by Koch. It was not, 

 however, until some years later that the method yielded 

 results of any practical importance, inasmuch as it was 

 at first almost exclusively applied by bacteriologists 

 whose previous information on questions of water-supply 

 was of a somewhat limited order, whilst the value of the 

 method for the solution of many hitherto unsolved prob- 

 lems connected with the hygiene of water is even now 

 but imperfectly appreciated by chemists. When the 

 method was first applied to the London water-supply, in 

 the year 1885, it at once brought to light that in the pro- 

 cess of sand-filtration, as practised on the large scale, 

 a most astonishing proportion of the micro-organisms 

 present in the unfiltered water were removed, whilst in 

 the best of our deep-well waters the number of microbes 

 found was so small that it seemed probable that the re- 

 moval of these low forms of life in this process of 

 natural filtration was really complete, and that the few 

 actually found had very likely been imported into the 

 wells from the surface. On the other hand, it was shown 

 that the sand-filters did not wholly remove the organisms 

 present in the unfiltered water, as, in the course of regular 

 examinations carried on over a period of more than three 

 years, a most unmistakable relationship between the 

 number of microbes present in the unfiltered and filtered 

 waters respectively was discernible. The scope of the bac- 

 teriological method of examination became very much 

 narrowed when it was discovered that there are many 

 micro-organisms which have the power of multiplying 

 to an enormous extent in the purest waters, including 

 distilled water itself, so that the number of microbes 

 present in a given sample of water affords no indication 

 per se of the purity or otherwise of the water. This dis- 

 turbing element in the bacterioscopic examination of 

 water is not sufficiently emphasized by the authors. But 

 this extraordinary phenomenon of multiplication, although 

 it invalidates the bacteriological process for the general 

 purposes of water examination, does not at all interfere 

 with its successful application to the investigation of the 

 efficiency of filtration, either natural or artificial, pro- 

 vided that the filtered water is subjected to examination 

 without delay after it has undergone the process of 

 filtration. 



It should be pointed out that there exists a very wide- 

 spread misapprehension as to the ideal object of the bac- 

 teriological examination of waters, and the authors of this 

 work fall into the same error to some extent also. It is 

 very generally supposed that the main object of a bacterio- 

 logical examination is to discover whether or not there 

 are disease-producing organisms, e.g. those of typhoid, 

 in the water. But this is a point really of very limited 

 importance, and what should be kept in view in an ex- 

 amination of water is the endeavour to discover, not 

 whether the water contains zymotic poison at the time 

 of analysis, but firstly, whether it is exposed to influences 

 which may at any time lead to the introduction of such 

 zymotic poisons, e.g. through contamination with sewage ;. 



