324 



SCIENCE-GOSSIP. 



to each other. Before leaving the pool it is 

 important to take a small quantity of the mud 

 from the bottom and put it into the test-tube with 

 the desmids. About as much as will cover the 

 bottom of tube by three-quarters of an inch will be 

 sufficient . Always choose a sunny day by preference 

 for collecting, for it is then the largest quantities of 

 desmids come to the surface, and may often be 

 seen as a green scum on the top of the mud. If 

 the day be dull and you take a small quantity of 

 the mud, the desmids 

 are sure to be found, 

 as will be later 

 described. 



The most con- cr 



venient method of 

 collecting the des- 

 mids from the sur- Fig- 2- 

 face of the mud at 



the bottom of the pools is by means of a large 

 pipette (see fig. 2). This is made with a piece of 

 quarter-inch or five-sixteenth -inch glass tubing 

 about seven inches long, and having fixed to the 

 top an india-rubber air-ball about one and a-half 

 inches in diameter. Such balls can be obtained from 

 dealers in photographic apparatus, as they are 

 largely used for pneumatic releases in connection 

 with instantaneous shutters of cameras. To use 



Test-tube Stand for Desmids. 



the pipette, press the ball to expel the air before 

 entering the water, and until the point of the tube 

 almost touches the surface of the mud. Then, on 

 releasing the pressure on the ball, as much water as 

 you desire will be sucked into the pipette and thence 

 conveyed into a test-tube. This pipette will be 

 found invaluable after some practice, as by means 

 of it clusters of desmids which can be seen growing 

 up from the mud in a thin filament can be sucked 

 up quite clean and without any adhering mud. It 

 is also a most useful tool to use at home in 

 changing desmids from one tube to another when 

 required. 



On reaching home, remove the corks from tubes, 

 and place them into a stand such as shown in 

 fig. 3. This is constructed with a block of wood 

 having holes drilled in it. The stand must be 

 of a suitable size to hold six tubes nine and 

 a-half inches long by two inches wide and one 

 and a-half inches deep, the holes being bored 



three-quarters of an inch deep and of a size to 

 ensure that the tubes will drop in freely. As 

 many stands may be made as desired. The size 

 given takes up little space, and will rest on a 

 window-frame or sill. 



Place the stand of tubes near a window ; if 

 facing the south cover the tubes with a piece of 

 gauze or muslin to prevent the growth of confervae 

 and keep the dust out of the tubes. In a day or 

 two the desmids will be seen growing in large 



clusters up the tubes, 

 when they may be 

 taken out perfectly 

 clean with a small 

 pipette for observa- 

 tion, or transferred 

 to a tube of clean 

 Pipette. rain-water for a few 



days. In this way 

 large quantities of perfectly pure gatherings may 

 be obtained. The desmids can often be observed 

 under the microscope, in situ, in the tubes, and 

 much valuable information obtained regarding 

 their growth. Use a low-power object-glass, not 

 less than one-inch. The convexity of the tubes 

 does affect the image, but on the line along the 

 centre of the tube sufficient view will often be 

 obtained, and the tube can be turned all round 

 for examination. Before putting a tube under 

 the microscope fill up with water and insert the 

 cork until the surplus water overflows. The 

 contents of the tube may then be examined 

 without disturbing the position of the desmids 

 growing inside. To facilitate the examination 

 of the tubes under the microscope, make a 

 small table (to rest on stage of microscope) out of 

 a piece of cigar-box wood, about four inches long 

 by two and a-half inches wide, with a narrow 

 piece half an inch wide, glued at right angles. 

 Against it the tube rests when the microscope is 

 inclined. Cut a round hole one inch in diameter 

 in centre to allow light from mirror to pass 

 through, (See fig. 4.) 



To transfer small quantities of desmids from 



Fig. 4. 



tubes to slides a small pipette made with a child's 

 feeding-bottle rubber teat on end will be found 

 very handy. These small pipettes can be obtained 



