of the Fishery Board for Scotland. 



333 



The jelly, still liquid, was then poured upon the plates in the usual 

 manner. 



In order to avoid the liquefaction of the jelly on the plate by the bacterial 

 growth, which is a great hindrance to proper enumeration, agar-agar jelly 

 might also be used. This jelly is not liquefied by bacteria, but it has the 

 disadvantage of having a high melting-point. In suggesting its use, two 

 methods occurred to us for trial, — one to melt the jelly, and allow it to 

 cool till it became semifluid, the other to pour the water upon a layer of 

 jelly, previously spread upon the plate, and allowed to cool, but not to 

 set completely. In the latter case it is necessary to dilute the water 

 under observation with a sufficient quantity of sterilised distilled water. 

 It was found possible to use the former method, the jelly retaining a 

 syrupy consistence after being allowed to cool to some degrees below its 

 melting-point, but it was not actually employed at the river side. 



The enumerations actually made were in water from the Tweed, near 

 Melrose, and the Dee, near Aberdeen. The following summary of the 

 results attained has been drawn up by Dr Woodhead and Dr Gibson. 

 Dr Gibson visited Melrose and Aberdeen specially, and succeeded in 

 making the plate cultivations within about six hours after collecting the 

 water. It need hardly be added that in each case these observations were 

 made subservient to the more important work of direct investigation of the 

 organisms. 



With water from the Tweed, taken near Melrose, there were three 

 series of enumerations, the results of which are of considerable interest, 

 and raise questions of very great importance. 



First series.— Water taken from the right bank of the Tweed, below the 

 cauld, on the 30th of April 1886. On the 3rd of May, the number of 

 points of growth was 3000 per c.c. of water. A few of these, number not 

 definitely stated, were moist. That the number was not large is evi- 

 denced by the fact that the liquefaction of the whole of the gelatine film 

 had not taken place on the 8th of May. 



On the same date water was taken from the mill-stream at Melrose, 

 near the sluice. Examined on the 3rd of May, the number of points (of 

 which one was a large liquefying area — there were also several smaller 

 liquefying points) corresponded to 600 per c.c. of the water. Liquefac 

 tion was not complete by the 8th of May. 



The next specimen of the same date was taken from the left bank of 

 the Tweed, above the cauld, where the stream runs very rapidly. In this 

 there were 3024 points per c.c. on the third day, only one or two of 

 which were liquefying, although there was complete liquefaction by the 

 eighth day. These observations were made when the rainfall had not 

 been great. 



Second series — The observations were made after there had been a 

 heavy fall of rain, and when the Tweed was consequently in flood. 



The water was taken on the 18th May 1886, from the right bank of 

 the river above the cauld. On the fourth day the points were so numer- 

 ous and the liquefaction was so extensive, that it was impossible to count 

 the centres of growth with anything like accuracy. It may be stated that 

 the approximate number of bacteria and spores, per c.c, would be about 

 12,000. The same difficulty was experienced with water taken at the 

 same time at the Chain Bridge below Melrose, on the left bank of the 

 river. In this case the approximate number would be 7500 per c.c. 



In water collected from the right bank of the Tweed, near the Hydro- 

 pathic establishment, there were 4120 per c.c. 



On this occasion the fourth specimen of water was taken from the right 

 bank below the cauld, where the water is somewhat stagnant. On the 



