Physiology

Bacteriophage.

An interesting phenomenon called after D'Herelle, its discoverer, has attracted much attention. When working with certain cultures of intestinal bacteria D'Herelle ob served that on occasions culture apparently failed, the broth remaining quite clear. Subsequently he found that addition of a minute quantity of one of these clear fluids to a culture tube, cloudy with growth, was followed by clarification of the latter ; as little as one part in a million was sufficient. He considered that he had obtained evidence of a filter-passing "microbe bacte riophage" and obtained the phenomenon by successive culture from intestinal contents, sewage, soil extracts. This clarifying power is a property of leucocytes, tears, nasal mucus, eggwhite and other substances.

From the first the filter-passing microbial explanation met with opposition, many authorities regarding the phenomenon as being due to the action of an autolytic enzyme, or a catalyst causing the micro-organisms to produce autolytic ferments. Later, Fleming described a somewhat similar phenomenon by means of a special micro-organism that he isolated (M. lysodeikticus). This organ ism in thick suspension is in a few minutes completely dissolved by tears in a 1-9,00o dilution and using it as an indicator he found evidence of the lytic principle in nearly all tissues of the body, but not in urine, cerebrospinal fluid or sweat. In the vege table kingdom he found it in the turnip alone. It is doubtful whether there is a single lytic substance or more than one. The essential difference between this and D'Herelle's phenomenon is that the former cannot be transmitted in series. Fleming there fore speaks of it as a "lysozyme," and points out that some bac teria are sensitive to lysozyme action and others not, thus raising the speculation whether the pathogenicity of bacteria may be de termined by the absence of lysozyme.

Filter-passing Viruses.

Since 1905 papers have appeared from time to time in medical literature on the "filter passer" or "filterable virus" (see FILTER-PASSING VIRUSES). A series of morbid conditions is now recognized with more or less certainty as being due to a virus so minute that it passes through the pores of a porcelain filter, or in some cases is beyond the lowest limits of microscopic vision. Of these diseases rabies, vaccinia and per haps variola, are the best known. In lethargic encephalitis and herpes, evidence is tending in that direction but is not conclusive owing to the discovery that laboratory animals mainly used for this type of work (monkeys, rabbits) may under normal condi tions present appearances in their brains that have been regarded as evidence of experimental transmission from man.

Dengue has been added to the list, while the so-called mosaic disease of the tobacco and tomato plants (see PLANTS : Plant Pathology) is stated to be due to a filterable virus, and distemper in dogs may show a like origin. In addition a transmissible filter passing virus has been recognized in the rabbit ; at first this virus was thought to be the cause of varicella but it is now recognized to be the cause of a naturally occurring infection of the rabbit.

Gye and Barnard have described and photographed by means of ultra-violet light, respectively, a filterable virus derived from certain malignant tumours, following in this direction the pioneer work of Rous on chicken sarcoma. (See CANCER RESEARCH.) Finally, in the opinion of some authorities the cause of influenza (see INFLUENZA) is not Pfeiffer's B. influenza, this being merely a usual concomitant, but is in reality a filter-passing virus that has not yet been determined with certainty.