of the Fishery Board for Scotland. 



183 



stages of its development. Some, for instance, which are light in colour 

 and moist when they first make their appearance, may become covered 

 with a thin dry wrinkled pellicle, which is usually somewhat darker in 

 colour. Further, several forms may have almost the same naked eye 

 appearances when growing on one nutrient medium, though their 

 behaviour on other media and their microscopic appearances may be quite 

 distinctive. 



For instance, on bread paste there grows a pink torula, a flesh-coloured 

 bacillus, and a small bacterium, also flesh-coloured. Again, there is a 

 yellow micrococcus amongst the species found, that cannot readily be dis- 

 tinguished from a yellow sarcina met with in both the Tay and Tweed 

 waters, when the two are seen growing on bread paste. In the case of 

 those organisms which liquefy gelatine, e.g. Bacterium termo. Bacillus 

 subtilis, Violet bacillus, Yellow sarcina, and many others, there are usually 

 distinctive features by means of which each may be recognised, especially 

 if we can observe their manner of growth on other nutrient media. Up 

 to the present only solid or jelly-like media have been used, but now that 

 a number of pure cultivations have been obtained it will be necessary to 

 observe their behaviour in fluid media. 



Forms of Bacteria Observed, 



The following descriptions will serve to indicate some of the various 

 forms of bacteria and allied micro-organisms (torula, sarcina) which 

 have been already isolated. Especial attention has been given to the 

 Tweed water. 



Great difficulty has been experienced in giving any adequate descrip- 

 tion of the colour and appearance of the organisms described. Thus in a 

 description it is impossible to state the various shades or tones of colour, 

 such as yellow. We have met with growths of all varieties of this colour, 

 pale honey colour, bright and dull gamboge yellow, orange, lemon, chrome, 

 and Indian yellow, and so on ; and in some cases it has been only on 

 seeing the growths side by side that a striking difference has been 

 apparent. White, yellow, and brown are the preponderating colours, 

 pink and red being next in frequency. 



The only way in which this difficulty can be adequately met in a report 

 is by a series of coloured drawings, which have not yet been com- 

 pleted. 



In the microscopic examination, the method of preparation was uni- 

 form, and although the slight contraction of the protoplasm, and some 

 other modifications, are produced by the preparation, it serves well for a 

 relative comparison of different forms, both as to characters and size. 



The examination and measurement was in all cases made with 

 Powell & Lealand's l-25th oil-immersion and Abbe's illuminating 

 apparatus. The ocular micrometers employed were Verick's, giving a 

 magnifying power of exactly 2000 diameters ; and Zeiss's screw micro- 

 meter, which was used to control the results more exactly. It is neces- 

 sary to mention these facts, as examinations made with lower powers 

 (e.g., X 850 or 1000) do not serve to determine with sufficient accuracy 

 the points of difference of nearly allied forms. 



It is proposed in a future report to give exact drawings to scale of the 

 more important forms, but for the present it has been thought sufficient to 

 state briefly the most striking characters and measurements. 



