is some evidence to show that certain bacteria-quite small, it is true, yet large enough to be seen with our ordinary microscopes-do pass through some of our so-called bacteria-proof filters. Their passage through these filters may be explained by their peculiar consistency which enables them to pass the pores that offer a complete barrier to some equally small but less plastic organisms. Wherry described a number of filtration experiments with the bacillus of guinea-pig pneumonia, using Berkefeld cylinders No. 5 and No. 8, and the Chamberland eylinder F. His first experiment was with Berkefeld No. 5, a vacuum of about 660 mm. being used. The filtrate was collected in five lots of about 25 c. c. each and placed in an incubator; only the two last portions collected showed growth. A second experiment carried out in the same manner resulted similarly, the only difference being that the last one only of the five lots collected showed growth. The organism did not pass through the large Berkefeld No. 8 nor through the Chamberland F filters. Wherry states that the bacillus of guinea-pig pneumonia is 0.5 μ wide and 0.7 μ long. This is the only record of a microorganism whose smallest diameter is not less than 0.5 μ having passed regularly through Berkefeld filters. Von Esmarch, in the course of his endeavors to ascertain the existence of ultramicroscopic saprophytes, isolated a very minute vibrio, which he named Spirillum parvum. This organism, from 1 to 3 μ long and 0.1 to 0.3 μ wide, passed through Berkefeld, Chamberland F, and other filters. Neither Wherry nor von Esmarch mentions the very important matter of the time required for their filtrations, and von Esmarch fails, in addition, to note the degree of vacuum which he employed. Borrel, in the course of certain filtration experiments with the virus of sheep pox, found that very minute water vibrios passed through certain bougies. He also found a minute protozoan 3 to 4 μ long and 0.25 μ broad. This organism was named Micromonas mesnili, and is said to be the smallest known protozoan. Borrel, however, used filters especially prepared and very much more porous than the Chamberland F, as has been previously explained. All of the organisms which pass these filters, however, are unusually small and actively motile. The size, consistency, and motility evidently all play a considerable part in determining the filterability or nonfilterability of microorganisms. By a series of ingenious calculations, Errera has endeavored to determine the limit in size of microorganisms. To use his own query, May there not be microorganisms as much smaller than ordinary bacteria as the ordinary bacteria are smaller than our largest trees? Errera's calculations, based upon the "atomic theory" and the weight of molecules, lead him to believe that it is impossible for living forms to exist which are less than one-fifth or one-tenth the size of Micrococcus progrediens. This micrococcus is the smallest known, measuring only 0.15 μ in diameter. Abbé and Czapski state that microscopes as they are now constructed will not permit us to distinguish objects smaller than 0.1μ, the difficulty lying in the illumination of the field rather than in the magnifying power of the lenses. Siedentopf and Zsigmondy have recently devised a new microscope which they claim has enabled them to distinguish particles which are completely invisible when the highest magnification of the ordinary microscope is employed. The essential feature in this new microscope consists in the method of illuminating the field. A powerful oblique light is thrown upon the objects in such a way that they become visible, appearing as minute luminous points. It is to be hoped that Siedentopf and Zsigmondy have brought forth a principle in the construction of microscopes which may be utilized in bacteriological investigations. The value of the researches herein described can not be overestimated. In addition to the light which they have thrown upon the etiology of certain infectious diseases, they have taught us that there are many disease-producing microorganisms which can pass readily through ordinary porcelain and earthen filters, and that one at least (that of horse sickness) is not withheld even by the finest-pored filter known. They have also taught us that clear fluids which yield no culture, by whatever method used, are not necessarily sterile, but may be very infectious and in the highest degree dangerous to men and animals. These discoveries indicate also that the fields of bacteriological research present unexampled opportunities for original investigations, and notwithstanding the great advances made during the last two decades there are yet greater things to come. A better knowledge of the etiology of a disease always leads to more intelligent and therefore more successful efforts to combat it. On this account we have reason to hope that these filtration experiments will not only increase our knowledge of the causes of maladies which are now so baffling, but that they will also enable us to do more toward their prevention and cure. BIBLIOGRAPHY. BEIJERINCK, W. Ueber ein Contagium vivum Fluidum als Ursache der Fleckenkrankheit der Tabaksblätter. Cent. f. Bakt., Jena, 2. Abt., 5. Bd., No. 1, p. 27-33. 15. Jan., 1899. BORREL, A. Expériences sur la filtration du virus claveleux. Compt. rend., Soc. de biol., Paris, tome 54, no. 2, p. 59. 24 Jan., 1902. BORREL, A. Microbes des eaux et culture d'un protozoaire minimal. Ibid., p. 61. BORREL, A. Etudes sur la clavelée; sérothérapie et séroclavelisation. Ann. de l'inst. Pasteur, Paris, tome 17, no. 11, p. 732. 25 Nov., 1903. CELLI, A., & BLASI, D. DE. Ist das Wuthgift filtrirbar? Deut. med. Woch., Berl., 29. Jahrgang, No. 50, p. 945-946. 10. Dez., 1903. CENTANNI, EUG. Die Vogelpest; Beitrag zu dem durch Kerzen filtrirbaren Virus. Bakt., 1. Abt., Originale, 31. Bd., No. 4, p. 145-152; No. 5, p. 182–201. and 27. Feb., 1902. DUBOIS, ALBERT, Cent. f. 14. Feb. Une maladie infectieuse des poules à microbes invisibles. Comp. rend., Soc. de biol., Paris, tome 54, no. 29, p. 1162-1163. 31. Oct., 1902. VON ESMARCH, ERWIN. Cent. f. Bakt., Ueber kleinste Bakterien und das Durchwachsen von Filtern. Bakteriologische Studien über die Aetiologie einer epidemischen Erkrankung der Hühner in Tirol (1901). Cent. f. Bakt., Jena, 1. Abt., 30. Bd., No. 16, p. 593-604. 7. Nov., 1901. LOEFFLER & FROSCH. Berichte der Kommission zur Erforschung der Maul-und Klauenseuche bei dem Institut für Infektionskrankheiten in Berlin. 23. Bd., No. 9-10, p. 371-391. 10. März, 1898. LOEFFLER. Bericht der Kommission zur Erforschung der dem Institut für Infektionskrankheiten in Berlin. 24. Bd., No. 15-16, p. 569–574. 28. Okt., 1898. MCFADYEAN, J. Cent. f. Bakt., Jena, 1. Abt., Maul-und Klauenseuche bei African horse-sickness. Journ. of comp. path. and ther., Edinburgh and London, v. 13, no. 1, p. 1-20. March 31, 1900. MAGGIORA, ARNALDO, & VALENTI, GIAN L. Leber eine Seuche von exsudativem Typhus bei Hühnern. I. Mittheilung. Zeitschr. f. Hyg. u. Infektionskr., Leipzig, 42. Bd., 2 Hft., p. 185-243. 1903. MARCHOUX, SALIMBENI ET SIMOND. La fièvre jaune; rapport de la mission française. Ann. de l'inst. Pasteur, Paris, tome 17, No. 11, p. 665-731. 25 Nov., 1903. MARX, E., & STICKLER, ANTON. Untersuchungen über das Epithelioma contagiosum des Geflügels. Deut. med. Woch., Berlin, 28. Jahrgang, No. 50, p. 893-895. 11. Dez., 1902. NOCARD ET Roux. Le microbe de la péripneumonie. Ann. de l'inst. Pasteur, Paris, tome 12, no. 4, p. 240-262. 25 Avril, 1898. NOCARD, E. La "Horse-sickness" ou "maladie des chevaux" de l'Afrique du sud. Bull. de la Soc. cent. de méd. vét., [8 sér., tome 8, no. 2] n. s., tome 19, p. 37-51. 30 Jan., 1901. REED & CARROLL. The etiology of yellow fever. A supplemental note. 3, no. 8, p. 301-305. Feb. 22, 1902. REMLINGER. Amer. med., Phila., v. Le passage du virus rabique à travers les filtres. Ann. de l'inst. Pasteur, tome 17, no. 12, p. 834-849. 25 Dec., 1903. REMLINGER & RIFFAT-BEY. Le virus rabique traverse la bougie Berkefeld. Compt. rend., Soc. de biol., Paris, tome 55, no. 21, p. 730-731. 19 Juin, 1903. REMLINGER & RIFFAT-BEY. Sur la perméabilité de la bougie Berkefeld au virus rabique. Compt. rend., Soc. de biol., Paris, tome 55, no. 25, p. 974-976. 17 Juillet, 1903. Roux & NOCARD. Le microbe de la péripneumonie. Cinquantenaire de la société de biologie; volume jubilaire. Paris, 1849-1899, p. 440–449. SANARELLI, G. Das myxomatogene Virus; Beitrag zum Studium der Krankheitserreger ausserhalb des Sichtbaren. Cent. f. Bakt., 1. Abt., 23. Bd., No. 20, p. 865-873. Juni, 1898. SCHÜDER. 1. Der Negri'sche Erreger der Tollwuth. Deut. med. Woch., 29. Jahrgang, No. 39, p. 700. 24 Sept., 1903. SIEDENTOPF, H. & ZSIGMONDY, R. Über sichtbarmachung und Grössenbestimmung ultramikroskopischer Teilchen, mit besonderer Anwendung auf Goldrubingläser. Annalen der Physik., Leipzig, 10 Bd., No. 1, p. 1-39. 1903. WHERRY, WM. B. Experiments on the permeability of the Berkefeld filter and the Pasteur Chamberland bougie to bacteria of small size. Journ. of med. research, v. 8, no. 2, p. 322-328. Nov., 1902. NEW FACTS CONCERNING THE ETIOLOGY OF HOG CHOLERA.a By E. A. DE SCHWEINITZ, M. D., PH. D., AND M. DORSET, M. D., Chief and Assistant Chief of the Biochemic Division, Bureau of Animal Industry. PRELIMINARY REMARKS. During the course of the investigations concerning hog cholera which have been carried on by the Biochemie Division of the Bureau of Animal Industry, certain outbreaks of that disease were met with which apparently were not produced by the hog-cholera or the swineplague bacilli. The disease was highly contagious and fatal to a large proportion of the hogs which were attacked. These observations, which were inexplicable previous to the researches herein recorded, together with the great variations in the physical symptoms and the postmortem lesions encountered in different outbreaks of so-called "hog cholera," have led us to institute experiments to determine, if possible, whether or not there are other infectious diseases among hogs in this country than those caused by the hog-cholera and swine-plague bacilli, and also to ascertain what was the etiological agent in those outbreaks of disease mentioned above, which apparently did not depend upon these bacilli for their. existence. These experiments have not yet been completed, but have gone far enough to enable us to publish this preliminary information. The outbreaks of disease which have furnished material for the study of the questions just outlined have all had their origin in southwestern Iowa, but, owing to the great distance of that point from Washington and the fact that it was not possible to establish a satisfactory laboratory in the field, it has been found necessary to expose a certain number of animals to infection in Iowa and then transport them by express to the Bureau Experiment Station near this city, where all the inoculations were made by the superintendent of the station. After once bringing the disease to Washington no trouble was, as a rule, experienced in perpetuating it by transferring from one animal to another. The experiments have reached such a stage that we feel justified in stating that there is an infectious disease among hogs in this country which can not be distinguished clinically from hog cholera, and which may be reproduced by infecting with material which contains no hog a The article in the main is published as Circulars Nos. 41 and 43 of this Bureau. |