containing undetected muscle sugar. Even when preliminary tests are made with some gas-producing bacillus there is still an opportunity for error, provided the tests are carried on only for a day or two. No bouillon should be judged free from sugar and safe for use until in fermentation tubes it has been subjected for at least a week to the influence of Bacillus cloaca or some other organism producing an abundance of gas from grape sugar. If at the end of this period no gas has developed, and the transfer of a loop of fluid from such a tube into another fermentation tube containing a dextrose-bouillon sets up an evolution of gas, then the first bouillon may be used with confidence. Again, if cane sugar is sterilized in an acid bouillon at least a part of it is inverted, i. e. changed into dextrose and fructose, and fermentation results obtained therefrom may be due to the presence of any one of three sugars. Bouillon should always be made distinctly alkaline before cane sugar is added. Many of the older fermentation experiments are worthless on account of neglect of such precautions, to say nothing of some recent ones. Again Bacillus tracheiphilus grows not at all or feebly on nutrient gelatine as ordinarily made, or in media which is acid beyond a determinable slight degree, and if only such media were used the erroneous conclusion might be reached that it could not be grown outside of the host plant, whereas it grows freely in artificial media, even on gelatine, when the right conditions are established. Bacillus amylovorus grows well in some gelatines and refuses to grow in others. Even comparatively slight changes in the acidity or alkalinity of the culture media often have a marked effect on the growth of certain organisms, while others, e. g., Bacillus cloacae, are able to grow in almost any medium. Many bacteria

prefer alkaline media, and some are very sensitive to the presence of acids, while a variety of bacteria commonly met with in water will not develop at all if the medium is rendered strongly alkaline. Other organisms grow well in acid media.1

14a For a striking illustration of the effect on the growth of water bacteria of comparatively slight charges in the reaction of gelatine, see a recent table by George W. Fuller, in a paper entitled: (13) On the proper reaction of nutrient media for bacterial cultivation.-Journal of the American Public Health Association, Concord, N. H., Oct., 1895, p. 393,

Even the slightly varying acidity of steamed slices from different potato tubers may exert a marked effect on the growth of certain sensitive organisms. On this account some bacteriologists have advised discarding the potato altogether. I have myself found the potato a very useful substratum for the growth of both fungi and bacteria. All comparative tests on potato ought, however, to be made on cylinders or slices cut from the same tuber, and in every case the reaction, acid, neutral, or alkaline, should be carefully recorded. The behavior of the organism on a variety of tubers should also be determined, before deciding that it is something new. It has been thought by some that the best nutrient substance for a parasite must be, unquestionably, the juices of the host plant but this does not follow since there are all grades of parasitism, and even if it did, there are several chances for error in its employment, e. g. the nutrient juices are usually sterilized by steam heat and this may cause a number of chemical changes resulting in a compound very different from the living plant and entirely unsatisfactory as a culture medium, as many have learned by experience. Again, for some particular reason, even the juices of the plant when sterilized at ordinary temperatures by filtration, may be less well adapted to the needs of the parasite than well made beef bouillon or ordinary nutrient agar. In general, the standard culture media of bacteriology should be tried first. Some bacteria can be cultivated only on special media or at special temperatures, or under unusual conditions. Bacillus subtilis will only grow in the presence of free oxygen; Bacillus amylobacter, B. tetani, and B. carbonis will only grow in the absence of oxygen. Winogradsky states that his nitrifying organism obtained from European soils will not grow in the ordinary culture media and thrives best in solutions of inorganic substances, and on silicate jelly. Bacterium tuberculosis can be cultivated only in bouillon and on blood serum and nutrient glycerine agar, and at temperatures above 30°C. Bacterium influenza also flourishes at blood heat and can only be grown, it is said, in the presence of red blood corpuscles or in media containing yolk of eggs; other organisms have thus far refused to be cultivated at any temperature or on any artificial medium, e. g. Bacterium lepræ and B. syphilitis. Some bacteria

are destroyed at temperatures at which careless workers frequently pour their agar plates, while others refuse to grow at ordinary temperatures or even at blood heat, grow best at 50°-60°C., and are not killed until the temperature exceeds 70° or even 75°C. Finally, a race of Bacterium anthracis incapable of producing spores has been developed by growing the organism in media containing phenol; another non-virulent race bearing swollen, terminal spores, "drumsticks," by growing the organism in compressed air; and still another race destitute of virulence by cultivating it at temperatures above 40°C. These are not exceptional cases, similar care being necessary in all directions if one would avoid erroneous conclusions.

Naturally, every successful experimenter will vary his culture media in all sorts of ways in order to learn as much as possible of the organism under consideration, but at the same time he will determine its behaviour on the standard media, and will keep a very careful record of all that he does. The bacteriologist should make it an invariable rule to repeat every experiment two or three times, at the very least, and generally after an interval of some months or years he should repeat all his experiments. Even then he will fall into errors enough. He certainly should proceed with as much care as the chemist, and in many directions the work passes naturally over into chemistry. If quantitative or volumetric analysis requires all sorts of precautions and excess of care to avoid errors, no less does this youngest of all the sciences.

A few words respecting the occurrence of bacteria in normal plant tissues will be in place before concluding these general remarks. It goes without saying that such minute and universally distributed bodies as bacteria are likely to be found at times almost anywhere, even in plant tissues which seem to be healthy, just as they may sometimes occur in the blood stream of healthy animals, but they are not normally present in the tissues of plants. All carefully conducted experiments have led to this conclusion. The reader who wishes fuller information may consult papers by Laurent, Buchner," Lehmann,16 14 (14) Sur la pretendue origine bacterienne de la diastase. Bull, de l'Acad. roy. de Belgique, T. X., pp. 38-57.

15 (15) Notiz betreffend die Frage des Vorkommens von Bacterien in normalen Pflanzengewebe. Muench med. Wochenschrift., 1888, pp. 906–907.

16 (16) Erklarung in Betreff der Arbeit von Herrn Dr. Hugo Bernheim, etc. Ibid, 1889, p. 110.

Fernbach" Vestea,18 Kramer,19 and Russell.20 Even when purposely introduced into living tissues they refuse to grow or spread but little and finally die out," unless they possess specific pathogenic power in which case the result is quite different.

The diseases which will be discussed in the following pages may be divided into four classes:

(1). Diseases of clearly established bacterial origin.

(2). Diseases which appear to be constantly associated with bacteria and which are probably due to some specific organism, but full proof of which has not been furnished.

(3). Diseases said to be more or less closely associated with the presence of bacteria and ascribed thereto, but in which little or no proof has been brought forward to establish the causal relation.

(4). Communicable diseases which have been ascribed to bacteria but associated with which no organism has been found and which are probably of non-bacterial nature.

On the whole it would perhaps be more logical to divide the following pages into four chapters in the way I have specified, but for practical reasons it has seemed better to discuss all of the diseases of a given plant in one place. I have, therefore, arranged the material by hosts, but will at the close try to summarize the whole subject in the manner above indicated.

It will certainly be some time, probably many years, before we have anything like a permanent scheme of classification for the bacteria. Our knowledge is still too incomplete. Meanwhile, we have to do the best we can with the present systems, all of

17

1 (17) De l'absence des microbes dans les tissus vegetaux. Annales de l'Inst. Pasteur, 1888, pp. 567-570.

18 (18) De l'absence des microbes dans les tissus. Ibid., 1888, p. 670–671.

19 (19) Bakteriologische Untersuchungen ueber die Nassfäule der Kartoffelknollen. Osterreichisches landw. Centralb. I, Heft 1, 1891.

20 1. c.

21 Lominsky: (20) On the parasitism when introduced into plants of some disease-causing microbes (Russian). Wratch., 1890. No. 6, pp. 133-135. Russell: 1. c.

Kornauth: (21) Ueber das Verhalten pathogener Bakterien in lebenden Pflanzengeweben. Centrb. f. Bakt., Parasiten-Kunde, u. Infectionsk, I Abt., Bd. XIX, No. 21, 8 Juni, 1896, pp. 801-805,

which are more or less arbitrary and unsatisfactory, and all of which are liable to be set aside at any time. I have here adopted Migula's system which seems to me very convenient, and on the whole the most satisfactory of any that has yet appeared.

Before proceeding to the body of this review it only remains to say that every effort has been made to deal impartially with the material in hand, and to present the essential ideas of the writers as concisely and accurately as possible. To this end the original papers have been consulted in every instance, unless otherwise stated in the text. So much vexation over wrong references has been experienced in time past by the writer that he has himself been at special pains to give full and accurate citations. It is to be hoped, therefore, that the reader will have no difficulty in finding the original papers. An endeavor has also been made to bring the subject fully up to date but it is quite likely that some worthy papers may have been overlooked, owing to the many languages and the ever increasing number of places of publication.

THE MEANING AND STRUCTURE OF THE
SO-CALLED "MUSHROOM BODIES" OF

THE HEXAPOD BRAIN.

BY F. C. KENYON, PH. D.'

In looking at a series of sections of the brain of a hexapod, especially of a hymenopteron, the most notable structures are two pairs, one to each side, of large cup-shaped bodies of "Punkt substanz," or, what in the light of our present knowledge of nerve structure is better denominated fibrillar substance. Each of these cups is filled to overflowing with cells having large nuclei and very little cytoplasm. From the under surface

:

22 Migula Schizophyta : (22) Schizomycetes. Die Natuerlichen Pflanzenfamilien (Engler u. Prantl). I Teil. 1 Abt. a, Lief. 129. 8vo. p. 44, Leipzig, 1896. This is the forerunner of a larger work soon to be published by Gustav Fischer, Jena.

'Clark University, Mass.