of the Fishery Board for Scotland. 



179 



drops are taken out with the pipette on the stopper, and transferred to 

 the gelatine. The bottle is reweighed, and the weight of the water is 

 obtained from the difference between the first and second weighings. 

 But this method has also disadvantages in practice. 



In addition to the estimation of the number of organisms in the water, 

 the points of liquefaction of the jelly are counted. And, as a further 

 step, separate cultivations from individual colonies can be obtained. 



The following estimates will serve as illustrations of the results ob- 

 tained : — 



Sample 1 of Tweed water (from Pavilion at Melrose), examined the day 

 after it was taken from the river. En water taken from near the bottom 

 of the stream there were 780 points of growth or colonies in '27 gramme, 

 or 2886 centres per gramme of water. In water taken from near the 

 surface there were 329 points in 0*27 gramme, or 1217 per gramme, giving 

 an average of 554-5 per 0'27 gramme, or 2053 per gramme. 



Sample 2. — In water taken from Drygrange there were 597 points in 

 0*27 gramme or 2209 per gramme at the first counting. Water taken 

 from below mid stream, at the second counting of a similar sample of 

 water, there were 603 points per 0*27 gramme, or 2232 points per gramme, 

 giving an average of 600 points for 0*27 gramme, or 2222 per gramme. 



Taking an average of the above countings, we find that Tweed water 

 contains 575 points of growth or colonies in 0*27 gramme, or 2134 per 

 gramme, each colony growing from a single bacterium or a single spore. 

 In addition to these, there may be several forms which grow extremely 

 slowly (so that they are not visible to the naked eye or with a low power 

 magnifying glass within six days), and others which do nob grow except 

 under water. 



Taking an average of the liquefying points, we find that there are 113 

 in 0*27 gramme, or 318 in each gramme of water. These liquefying 

 points are probably for the most part due to bacterium termo and hay 

 bacillus. 



It has been found by repeated experiments in Berlin, London, and else- 

 where, that good drinking water seldom contains more than 1000 points 

 or colonies in a single gramme ; in other words, that there are not more 

 than 1000 bacteria or spores of fungi in each gramme. Looking at it from 

 this point of view, the Tweed water is far from satisfactory, as in it we 

 find during the month of March an average of no less than 2134 points 

 per gramme. It is important to note the month or time of year in this 

 connection, for in some experiments made last year in the Gesundheitsamt 

 (Laboratory of the Board of Health Office), Berlin, on unfiltered river 

 water, it was found that during the winter there were far fewer organisms 

 than during the summer months (extremes, 685 in February and 3251 in 

 October, giving a mean number of 1435 for the year), so that when the 

 examination is continued we may expect to find a larger number of micro- 

 organisms in the Tweed during the summer months."^ 



It may be pointed out that after filtration the Berlin river water showed 

 an average of only 197 points of growth, 277 being the highest and 21 

 the lowest numbers recorded. This fact is well worth most careful con- 

 sideration. 



Another point to be carefully noted is the comparatively large number 

 of organisms near the bottom of the stream as compared with the surface. 

 This, of course, can be partially explained by the subsidence of particulate 



* In order to an exact comparison a more rigid control of the precise length of 

 time after taking the water from the stream is necessary. We were ui.able to ob- 

 tain favourable enough conditions for these observations, which should if possible 

 be done on the spot. 



