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RESUME. La Microsporidie Nosema bombycis, Protozoaire parasite agent de la pebrine du ver a soie, a eteetudiee cytochimiquement a la fois en microscopie photonique et electronique. Les examens ont porte sur la detection et la localisation des acides nucleiques (ADN et ARN), des polysaccharides, de la phosphatase acide, au cours des differents stades du developpement dans les cellules de I'hote (du schizonte a la spore). Les principaux resultats concernent les observations relatives aux polysaccharides et a la phosphatase qui ne sont detectes qu'au stade de la spore et ne sont pas observes au stade du schizonte. Les polysaccharides sont presents au niveau du sac polaire, du filament polaire et sur la membrane cytoplasmique; la phosphatase acide est localisee au niveau du sac polaire, du filament polaire et dans la vacuole posterieure. SYNOPSIS. Nosema bombycis, agent of pebrine disease of silkworm, was studied cytochemically, using both light and electron microscopy. Presence of nucleic acids (DNA and RNA), polysaccharides, and acid phosphatases was demonstrated and localization of these substances was determined in various stages of the parasite (from the schizont to the spore). DNA and RNA were detected in all these stages. Polysaccharides and acid phosphatase were found in the spore but not in the schizogonic stages. Polysaccharides were detected in the polar cap, the polar filament, and the limiting membrane of the cytoplasm of the spore. Acid phosphatase was found in the polar cap, the polar filament, and the posterior vacuole.

When a queen honey-bee becomes infected with Nosema apis, the result can be very serious indeed for her colony. The metabolic processes are disturbed by the damage done by the parasite to the epithelial cells of the mid-gut, and this apparently leads to severe damage to the ovaries, at first by the production of a high proportion of eggs that fail to hatch, and ultimately by complete cessation of ovi-position and supersession or death of the queen. In the case of Nosema bombycis, which attacks the silk moth, infection is carried from the female to her offspring via the egg; but there is no evidence that this ever occurs in the case of Nosema apis. Although large numbers of eggs, larvae, and pupae produced by infected queen honey-bees were examined, none was found to be infected with any stage of Nosema apis.

Among the new facts discovered in the course of the writer's investigation on the function of the polar filament of the spore of Nosema bombycis (Ohshima, 1927), the following two are considered the most important:(1) As soon as its filament extrusion is accomplished in the midgut of a silkworm, the spore discharges a viscous fluid through the tube of the filament. This fluid remains hanging in a spherical shape at the extremity of the filament.(2) Both the polar filament and the viscous fluid are speedily digested by the digestive ferment of the silkworm in a few seconds.

The epizootic pattern of pebrine within a colony of the silkworm, Bombyx mori (Linnaeus), was investigated. The rate of infection was high in the first, the second, and the fifth instars, and low in the middle instars. This pattern corresponded to the change in the number of larvae excreting spores of Nosema bombycis Naegeli.

Aside from Nosema bombycis Nageli, no other Microsporidian has received so much attention of investigators as Nosema apis Zander. A disease of adult honey bees for which the Microsporidian is responsible, and which is known by different names such as Nosema-Seuche, Isle of Wight disease, Nosema disease, etc., has been reported to occur in various parts of the world. In North America, White (1914) found 40 infected bees in 120 samples received from 27 states of the union, and two diseased samples received from Canada. The same author further published (White, 1919) valuable results of experiments on the means by which the spores may be killed. The morphology and development of the Microsporidian have, however, been studied by but three investigators, i. e., Zander (1911) and Fantham and Porter (1912). According to these authors, the spores of Nosema apis are on the whole similarly constructed to those of Nosenma bombycis studied by Stempell (1909). Recently, I had an opportunity of studying the Microsporidian, and have obtained more or less different results by observations upon the structure of the spore from those of the above mentioned European investigators. I shall briefly describe the results in the following pages. In a field at Spring Valley, New York, 660 workers of Apis millifica were collected from August 27 to September 5, 1920. Although I could not trace the hive for these captured bees, there were a number of hives in the nearby woods where the collection was made. The digestive tract of each bee was drawn out from the body by means of a pair of forceps and a needle. A part of the ventriculus was smeared on a slide and examined microscopically in the fresh state.