August 4, 1887] 



NATURE 



zn 



The book treats of microbes from every aspect, mor- 

 phological and physiological. The relation of microbes 

 in general to the nutritive media, their chemical products, 

 and the relation of these to the microbes themselves ; the 

 production of soluble ferments by them ; the influence of 

 light, heat, &c., are passed in review and treated fully. 



The pathogenic organisms are next considered. Their 

 relation to the animal body ; the means by which they 

 gain access to the animal system ; the various influences 

 commonly understood to constitute " predisposition " ; 

 the relation of pathogenic bacteria to food, air, soil, and 

 water ; the adverse influences, such as heat and light, 

 disinfectants and antiseptics, &c., are all discussed with 

 great lucidity and thoroughness. 



There is hardly any aspect under which the study of 

 pathogenic microbes — including the question of attenua- 

 tion — presents itself, which is not discussed in this volume. 

 The arrangement of the subject-matter is systematic, and 

 the method of treatment does great credit to the author, 

 inasmuch as he is, as far as possible, objective. He 

 carefully weighs and sifts evidence, and does not disdain 

 to make references to the literature of England and 

 France. He has, in fact, carefully read the literature of 

 this country on infectious diseases, and thus attests that 

 he is not guided by that spirit of narrowness which one 

 often meets with in modern German works. 



An English translation would, we have no doubt, be a 

 valuable addition to our own literature. E. Klein. 



Photography of Bacteria. By Edgar M. Crookshank, 

 M.B. (London : H. K. Lewis, 1887.) 



Since Koch first employed photography in bacteriology 

 ("Biol. d. Pflanzen," 1877, ii. 3) various attempts have 

 been made in this country and on the Continent to 

 advance the methods of photographing microscopic 

 objects, such as Bacteria, with high magnifying powers. 

 About fifteen years ago Dr. Woodward, of Washington, 

 published photographic plates of histological objects 

 taken under tolerably high magnifying power (400 and 500 

 diameters). These plates were brought out by the 

 Surgeon- General's Office, Army Medical Museum of the 

 United States : they attracted at the time a good deal of 

 attention owing to their comparatively high excellence. 

 That good photographs of histological and other micro- 

 scopic objects are of great value in themselves, owing to 

 their exactness, and the various advantages for purposes 

 of publication, may be taken as requiring no further proof, 

 and it seems equally obvious that indifferent photographs 

 are of less value than accurate drawings. 



Now, comparing Dr. Crookshank's photograms of histo- 

 logical and bacteriological objects, published in the 

 present volume, the former with those of Dr. Woodward, 

 the latter with those of Koch, there can be little doubt 

 that no real advance has yet been made in producing 

 photograms that are to take the place of accurate draw- 

 ings. By saying this I do not mean to convey the im- 

 pression that in Dr. Crookshank's volume there are not 

 some good photographs — vide his Plate XVI., further his 

 Figs. 7, 8, 30, 35, and 45, all of which are really fine in 

 many respects — but taking photography as a whole, as 

 applied to the representation of microscopic objects under 

 high powers, I think that the time has not yet come 

 when it can be said to have supplanted good and accurate 

 drawings. In connexion with this it must certainly appear 

 remarkable that in the numerous and important publica- 

 tions on Bacteria by Koch and his pupils since 1877 to 

 the present time we do not find a single illustration 

 represented by micro-photography. All their published 

 illustrations are drawings. 



With the new apochromatic objectives and projection 

 eye-pieces by Zeiss better results may be looked for, and 

 Dr. Crookshank, with his great skill in, and knowledge 

 of, the technique, will, we have little doubt, be able to pro- 

 duce them. 



As a clear and detailed account of practical micro- 

 photography. Dr. Crookshank's book is of great merit, 

 and will prove very useful and important. As the first 

 treatise on the subject in any language it is sure to com- 

 mand a high place. E. Klein. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he tinder- 

 tdke to return, or to correspond with the writers of, 

 rejected manuscripts. No notice is taken of anonymous 

 com munications. 



[The Editor urgently requests correspondents to keep their 

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 is so great that it is impossible otherwise to insure the 

 appearance even of communications containing interesting 

 and novel facts.'] 



The Sense of Smell in Dogs. 



It is, I think, of some interest to supplement the very striking 

 and exact experiments of Mr. Romanes on the scent of dogs, by 

 an account of some experiments of a like kind made with a very 

 different kind of dog, viz. a pug bitch. She was taught to hunt 

 for small pieces of dry biscuit in a good-sized dining-room. The 

 dog was put out of the room and a small piece, not much bigger 

 than a shilling, of dry Osborne biscuit, was hidden ; and as long 

 as the hiding-place was accessible to the dog she never failed to 

 find it. Sometimes the biscuit would be placed under a heap of 

 a dozen or more newspapers on a dinner waggon, sometimes 

 under a footstool, or sofa-cushion, or fire-shovel, and on two or 

 three occasions in the foot of a boot which had been just taken 

 off, the hiding body being always carefully replaced before the 

 dog was admitted into the room, and without exception the 

 biscuit in a very short time was discovered. It was over and 

 over again proved that the dog did not follow the trail of the 

 person who had hidden the biscuit ; often the dog went by a 

 different route, and in some cases one person hid the biscuit and 

 another opened the door. 



The experiment which has now special interest is the following 

 one. A small piece of biscuit was placed on the floor under the 

 centre of a footstool which was one foot square and six inches 

 high, and standing on feet which raised it one inch from the ground. 

 The dog, from the way in which she would set about moving the 

 stool, not a very easy thing to do, as it stood in an angle of the 

 wall, was evidently certain that the biscuit was \ eneath, and as 

 scent seemed the only means by which she could have come at 

 this conclusion, I thought to entirely mask this scent and prevent 

 her finding the biscuit by pouring eau-de-Cologne on the stool. 

 I found, however, it had no such effect, the biscuit was as readily 

 and surely found when the eau-de-Cologne was there as when 

 absent. It seems, then, that not only well-worn boots leave 

 behind a recognizable odour, as Mr. Romanes proved, but also 

 that to us at least so odourless a substance as dry plain biscuit 

 emits so much and so characteristic a smell that it immediately 

 spreads, even through considerable obstacles, to a distance of 

 several inches in a few seconds, for in most cases the biscuit was 

 found in thirty to sixty seconds after it had been hidden ; thus 

 time was not allowed, one would think, for all the surroundings 

 of the hiding-place to become saturated with the scent. 



W. J. Russell. 



Units of Mass, Weight, and Force. 



Might I venture to suggest to Prof Greenhill that it would 

 be very interesting to mathematicians, and jirobably would throw 

 great light on the above subject, if he would give us quotations 

 from some work by a practical engineer in which the idea of 

 inertia distinctly appears. Or, failing this, perhaps Prof Green- 

 hill could give practical instances (other than problems in 

 gunnery) in which mass quite apart from weight enters into 

 the engineer's calculations. 



It seems to me that many practical engineers never have 

 occasion to deal with acceleration, except that of circular motion, 

 and consequently only need to consider the weight of stuff, and 

 have no use for the dynamical unit of force. 



Gonville and Caius Collie, July 23. John B. Lock. 



