It is generally conceded that the plankton of tropical and sub-tropical seas is far less in quantity than that found in colder waters.The zoö-plankton depends ultimately for its food on the phyto-plankton; hence any factor limiting the growth of the phyto-plankton, which is capable of functioning in tropical and not in temperate or Arctic waters, might offer an explanation of this phenomenon. It has been shown by various investigators that this factor is not temperature, light, or salinity, and it has been suggested that the explanation may lie in the relative deficiency in tropical seas of the nitrates or nitrogenous compounds which are so essential for all plant life. A matter of common observation in support of this view is the remarkable scarcity of algal growth in the shallow waters of tropical shores as compared with that in similar situations in temperate regions, and the fact that in the tropics, wherever sewage or other nitrogenous waste is poured into the sea, a free growth of algæ is found.
In one of the tanks at the Plymouth Laboratory containing pipe-fish and sticklebacks, a whiting was found recently which exhibited black specks scattered over its pigmented areas and on the conjunctiva. The spots were fairly evenly distributed and averaged .5 to .1 mm. in diameter. Around each black point there was a clear unpigmented area.
In the following notes no attempt has been made to enter into the pathology or etiology of the diseases described, as only isolated cases have been available for investigation.I am much indebted to the Council of the Marine Biological Association of the United Kingdom for their kindness in granting me a table at their Plymouth Laboratory.
METHODS.THE methods employed in these experiments were mainly those used and described by Carrel and Burrows (1911 s, in a paper entitled ' I The Cultivation of Tissues in vitro, and its Technique." Since the successful cultivation of tissues outside the organism is largely dependent on close attention to details of technique, and these details are not entered into in Carrel's and Burrows' paper, the methods employed will here be fully described.I n investigations such as these the highest degree of asepsis has to be preserved when making cultures ; accordingly, since a laboratory built on the lines of a modern operating theatre was not available, a room was prepared in the following manner. The floor, tables, walls, ceiling, and windows were thoroughly washed down with hot water, and when dry were coated with an oily preparation, " dust allayer," such as is used for dressing wooden floors ; all ventilation shafts were closed and all draughts carefully excluded. The air thus rendered stagnant allows any spores of bacteria or moulds present to settle and adhere to any part of the oily surface of the room with which they may come in contact. Before these precautions were taken a large proportion of the tissue cultures were spoilt owing to the development of species of moulds, the spores of which are easily distributed by the least movement of the air. After treating the room as described, the development of a mould in a culture was of the rarest occurrence, and less than 5 per cent. of the cultures became septic through the growth of bacteria.Before proceeding to make a series of cultures the room is filled with steam given off from a number of vessels in which water is kept boiling during the whole course of the operation. The floor is freely sprinkled with water, and the mork-bench covered with sterile cloths. The condensed steani keeps moist all the surface of the room, and the risk of dust or the spores of bacteria and moulds interfering with the work is minimised.A necessary preliminary is the preparation of a number of pipettes made from glass tubing : these are drawn out at one end into a capillary, then comes Received February 25, 1913.
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