198 THE MICROSCOPE. 



est particle of colouring matter, either carmine OP 

 indigo. Mr. Thomas Bolton 1 directs a small quantity 

 of either of these colours to be rubbed up in a little 

 water in a watch-glass, and a portion taken up on the 

 point of a brush, and the brush run along the top 

 of the water in a trough; sufficient will be left 

 behind to barely tinge the water with the colour, but 

 this will gradually subside over the rotifers. Under 

 the microscope this minute quantity will be seen like 

 a rising cloud of dust, which as soon as it comes 

 near a rotifer is whirled round in definite curves, 

 showing at once the action of its wonderful coronary 

 cilia. This colouring matter is greedily devoured by 

 these creatures, and may be followed from the mouth 

 to the digestive canal. If rotifers or infusoria are 

 already in a cell and under a thin cover, a drop of the 

 mixed colour may be placed at the edge of the cover- 

 glass, and a piece of blotting paper touched at the other 

 side will draw a current through the cell. The cilia 

 and fine flagella on many of the small protophytes and 

 infusoria, which are very difficult to see while they are 

 in full activity, are easily seen when dying or after 

 death from a drop of iodine. The effect of colour- 

 ing matter on Volvox globator, Euglena viridis, and 

 Protococcus pluvialis is very interesting ; besides show- 

 ing the cilia, it brings out many histological specialities, 

 which are otherwise invisible. Aniline dyes are occa- 

 sionally useful for colouring. Osmic acid is used for 

 killing infusoria quickly in their expanded condition, 

 and they may afterwards be stained advantageously 

 with picrate of carmine. The most useful aquaria for 

 preserving and breeding minute organisms is the 

 ordinary confectionery cake-glass inverted. A square 

 block of wood (8 in. square) with a hollow turned 

 in the centre is required to receive the knob. It 

 should be covered with a round glass to exclude the 

 dust. 



For finding or selecting minute animals, or dis- 

 secting botanical specimens, the Houston-Browning 



(1) Mr. T. Bolton, of 57, Newhall Street, Birmingham, furnishes interest- 

 ing tubes of living specimens for the microscope at a trifling wst to hi 

 torrespondents. 



