of the Fishery Board for Scotland. 



335 



parison of the numbers of micro-organisms present (which correspond very 

 exactly with the proportion of albuminoid ammonia) at any given point in 

 the river. 



This holds good only after a rainfall more or less heavy. After a long 

 spell of fine weather, as has been noted, the general results are remark- 

 ably constant. The importance of this in relation to the salmon fisheries 

 is very great indeed. 



The River Dee. 



In this series of observations, exactly the same precautions were taken 

 ay in the jjrevious set of experiments on Tweed water. 



The water was obtained from the left bank of the Dee, above the Old 

 Bridge at Aberdeen, above the brackish water of the estuary. 



On the 17th July 1886, twelve gelatine tubes were inoculated with the 

 water. The tubes were kept from the light, and as cool as possible. 

 Within seven hours, plate cultivations were made, and these were 

 examined on the 20th July, three days after the water was taken. 



1. No. of points per c.c, ..... 1500 



2. „ ..... 1000 



3. „ 1650 



5. „ ..... 1500 



6. „ ..... 1000 



7. „ 1125 



8. „ . ..-,;/ V ', soo 



9. „ 500 



10. „ 1500 



11. „ 1300 



12. „ ..... 1625 



It will be seen that the numbers range from 500 per c.c. to 1650 per 

 c.c, giving an average of 1177 per c.c. These results, as compared with 

 those obtained on the Tweed, are very satisfactory indeed, especially as 

 the conditions are, if anything, in favour of the Tweed water. How these 

 results compare with the prevalence of salmon disease we must leave to 

 experts to decide, but the difference is certainly very remarkable. 



Section II. — Study of Special Bacteria and Allied Organisms. 



The next branch of the inquiry relates to the organisms present in 

 the water, what kinds are to be found, what is their life history, and 

 how they may be detected and identified. 



We pointed out in the previous report that this question — the separation 

 and special study of the organisms present — was essential to the proper 

 understanding of their relation to diseases affecting fish. From what 

 we know of the vast number and variety of bacteria alone, not to speak 

 of other low forms of fungoid life, we can scarcely hope to discover or 

 determine all the species which may be present in water. But, as in the 

 case of the air, there are certain species which are common, and are found 

 almost universally. Some Sarcinae and Micrococci amongst bacteria, and 

 some common Hyphomycetse, such as Pencillium Glaucum, and Mucor 

 Mucedo, may be found almost everywhere in the air. So in river water 

 we should expect that some would be commonly or almost constantly 

 present ; others of rare occurrence. 



We should thus hope, by determining the common species, and by 

 2u 



