look with suspicion upon a painted bacteriologic atlas. We hope, however, that the unprejudiced critic will concede that for certain objects (stab, streak, and potato cultures) a well-colored representation surpasses the best photograph, and that for a second group of pictures (platecolonies slightly magnified) a drawing, which can alone do justice to the depth of the object, is at least equal to a photograph. We gladly acknowledge that for the representation of individuals magnified 1000 times photography is the best method; but there is now scarcely any doubt that for the practical differential diagnosis of bacteria, only in somewhat rare cases is the picture of the individual of primary importance. We have, moreover, sought to take advantage of the photographic method when the individuals were to be represented, by comparing the splendid photographs in the atlas of C. Fränkel and R. Pfeiffer, and also those in the literature (by Löffler, Heim, Roux, etc.), with our own preparations.

The choice of varieties for illustration was often very difficult. To our great pleasure, we were able to present, with the exception of about 4 per cent., only originals in the atlas; while, naturally, those required as supplements to the text are more often copies. In the latter case the original source is always given. Varieties important from a medical standpoint, especially when they present any visible characteristics, could scarcely be omitted; also, almost all varieties pathogenic for animals are introduced. Chromogenic, zymogenic, and saprogenic bacteria were never, to our knowledge, so extensively represented before; nevertheless, in this portion a careful choice was required. We acknowledge that some among those selected might have been omitted, and others chosen.

The text is divided into a general part, which I have prepared alone, and a special part, in which I have received the constant cooperation of Dr. Neumann.

The general part furnishes a condensed survey of the principal properties of bacteria so far as they are of practical value, especially so far as they are of diagnostic aid. It is assumed that the reader has mastered the ordinary elements of bacteriologic technic, but at the request of the publisher we have appended a short list of media rules for

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stains, etc., and constant reference is made to them. complete information in these matters is furnished by the well-known works of C. Fränkel, Günther, Hüppe, and in especially painstaking minuteness by the exhaustive work of Heim: "Lehrbuch der bacteriologischen Untersuchung und Diagnostik."

The special part attempts to give, so far as possible in a natural botanical arrangement, a complete description of the important varieties, with constant reference to less important ones which for any reason are worthy of notice. Those which we have described in detail we have also thoroughly investigated, thus supplying many previous omissions. 1 A great part of the related species have been studied so far as time, strength, and opportunity allowed.

Of new "species," we have introduced only a very few; identical varieties described under various names we have grouped together; and in many places we have directly tried to build up a natural system. It was evidently impossible to offer anything complete or final in the treatment of the non-pathogenic varieties.

Moreover, we are of the opinion that the advance of bacteriology, which we seek, especially the elucidation of the questions of variability, relation, distribution in and outside of living organisms, etc., cannot be accomplished by one or several, but only by systematic national—or, better, international-cooperation of investigators under a grand division of labor. One task for this cooperation would be to so improve and remodel the present often unprecedentedly arbitrary and unscientific nomenclature of fission-fungi that it will not challenge the derision of every scientist. (Compare Introduction to Special Part.)

Not infrequently our observations did not agree with certain statements of various respected observers, but we have always expressly acknowledged the same, and especially have pointed out the contradictions and defects, hoping thus to do service.

For an extensive reference to literature we have found no

1 If this were conscientiously done by all editors of bacteriologic works, there would be at least a partial elimination of the varieties which are non-critically enumerated, absolutely insufficiently described, and often repeated under different names.

room, but have only employed citations to facilitate detailed studies, especially pointing out recent reviews with numerous references. Every bacteriologic investigator will be unable to dispense with the aids which we have employed: Centralblatt für Bakteriologie und Parasitenkunde (Redakteur Uhlworm, Kassel, seit 1887), Baumgarten's Jahresbericht über die pathogenen, und Koch's Jahresbericht über die zymogenen, etc., Organismen. By their comprehensive index they quickly furnish a complete abstract of literature.

If we have been able to somewhat further the diagnosis of bacteria, to lighten the task of the beginner, to indicate the numerous difficulties of this work, which are partly undetermined and too little appreciated, then we are rewarded for the great labor which we have expended. We hope especially to furnish the student in bacteriology a substantial aid, and to make it possible for him to better appreciate what is seen and heard. We beg our critics not to censure too strongly defects and mistakes, which necessarily entered because of the enormous material.

PROF. DR. K. B. LEHMANN.

PREFACE TO THE SECOND EDITION.

SOONER than we dared to hope, a large German edition of this work has been exhausted; the English, Italian, and Russian editions also have found a large sale. We accept this as an indication of the practical value of the book. With special pleasure we have observed in the numerous reviews of the book that its reformative tendency in regard to the grouping of varieties of bacteria, the strict division of the system especially, the rational naming of bacteria, etc., have found warm praise. The text-books of Heim and Mez have accepted our nomenclature entirely or in part. For many new names in Flügge-Kruse's work, which appeared a few months after ours, according to the rule of botanical systems, the priority remains with us. Moreover, where we have found that properly selected names, older than those which we chose in the first edition, existed, we have naturally strictly adhered to the rule of priority. We affirm with pleasure that, because of our exact observations and of reliable statements in the literature, the carefully championed view of the exceedingly great variability of bacteria finds more and more recognition, and that the authors who to-day describe "new species" are in the main fewer, as is witnessed by the intelligent views advanced by the collection of bacteriologists in New York in 1895 (C. B. xx, 450).

The opinion advanced from an esteemed source, that the constant emphasis of variability, of the limits of our knowledge, and of the uncertainty of known methods, may sometimes discourage the beginner, may not be entirely unfounded. Yet we believe this absolute frankness to be an advantage, even if thereby the dogmatic sharpness of the statements should sometimes suffer. With beginners one

may and must leave much unsaid in order not to confuse; but ever so short a text-book can only claim the designation of science if the student can follow the author's thoughts. Besides, for the learner there is no greater satisfaction, when he comes upon difficulties, than the certain statement that, in a certain point, the imperfection of our knowledge, and not his inability, is the cause of the difficulty.

The fruitful labors of all investigators in the field of bacteriology made necessary a complete revision of the text in both the general and special parts. In the general part the discussion upon the causes of disease, disposition, and immunity is substantially extended. Beginning with page 119 is an exposition of the most important botanical points of view which are important in classifying and properly naming fission-fungi. In the special part, in fifty varieties dependent upon autopsies, we have made additions and improvements; about eighty varieties are newly introduced. We have especially undertaken fundamentally new work upon the causes of diphtheria and tuberculosis, together with the related varieties. It is hoped that the value of the atlas is essentially increased by the introduction of nine new plates, which replace three old ones (diphtheria and the allied bacteria, varieties related to the tubercle bacillus, gonorrhea, and pest).

The literature of the past three years has been conscientiously studied; many statements are substantiated, and everything which seemed of importance in the publications up to about June, 1899, is taken up. We hope that we have made a proper selection from the almost immeasurable material, which increases daily. Perfection, naturally, we cannot expect: some small mistakes and oversights could not be avoided. The division of the work was the same as in the first edition.

K. B. LEHMANN.

R. O. NEUMANN.