smears were counterstained with eosin or Bordeaux red to bring out the cilia of Peritricha. Destaining was effected with iron alum (0.5 per cent.) or a saturated solution of picric acid in distilled water, overnight treatment with the latter reagent giving particularly good results with ciliates. Either Canada balsam or Stafford Allen and Sons' neutral “Sira” medium were used as mountants.

During the project, a need was felt for a technique by means of which wet-fixed material could be stained and mounted in the field—for smears on cover slips stored in liquid preservatives inevitably become more or less damaged by rubbing against one another while in course of transportation. This was found to be particularly so with gill smears, preparations from fishes heavily infested with trichodinids often having few if any of these ciliates remaining intact on return to the laboratory at the conclusion of a field trip. It was found possible to deal with a substantial amount of such material in the field, without undue loss of collecting time, by means of the following technique.

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Sets of 4″ by 1″ shell vials filled with iodized water, iron alum mordant, Shortt's haematoxylin, picric destaining reagent, alcoholic eosin and the various grades of alcohol and xylol required for dehydrating and clearing, are made up in the laboratory and stored in order in portable racks. Each of these vials will accommodate four 7/8″ square cover slips in a vertical series at right angles to one another. Staining may be carried out at the field base at the end of the day's collecting activities, the cover slip smears (already fixed in Worcester's mixture as modified by Davis) being immersed in the iodized water, mordant and stain for half an hour in each case, and allowed to remain in the picric acid overnight. The latter reagent is slow in action, and excessive destaining of trichodinids does not readily take place in it. Excellent results are obtained with these ciliates when so treated for from 8 to 10 hours. With practice the smears may be rapidly counterstained, dehydrated and mounted on the following morning without the necessity for microscopic checking. A further batch of smears may be mordanted overnight, stained on the following morning while the first batch are being mounted, destained during the day and mounted in the evening. Six staining sets made up as above and providing for the daily simultaneous preparation of two batches of 24 finished protozoan mounts from as many individual fishes, may be accommodated in a light plywood case measuring only 15″ by 8″ by 5″.

Internal organs, to be examined later for Myxosporidia, may be dissected out in the field and preserved in bulk in formalin. In the case of small fishes, the entire contents of the gall- and urinary bladders may be mixed with polyvinyl-acetic-alcohol (P.A.A. medium) on a microscopic slide, and covered with a cover slip. This method is a particularly good one for the preservation of fully extended trophozoites, and lends itself to use in the field. It was unfortunately not tried out until recently, and was thus not employed during this investigation, but is mentioned here for the information of future workers.

When dealing with fresh preparations in the laboratory, methyl green, neutral red and Lugol's iodine were used as intravitam stains. Bond's (1938) method of using 5 per cent. phenol proved most satisfactory for bringing about the extrusion of the polar filaments of myxosporidian spores. A dark ground condenser often proved of use, particularly in the study of peritrichous ciliates. All the figures were drawn with the aid of an Abbé camera lucida.