Dipping-tubes are used to take up small aquatic animals from the vessels in which they are kept. Very little practice will render the use of this instrument easy. The tube is held firmly between the thumb and the third and fourth fingers of either hand, while the index finger is pressed firmly on the top. Most people naturally prefer the right hand, but it is well to accustom oneself to use the right or left indifferently. The open end is then put into the water, just over the object to be secured, and the index finger lifted. The rush of water into the tube will carry the object into it, and if the finger be again applied to the top, the pressure of the atmosphere will prevent the water from escaping when the tube is lifted out[5].
Small brushes are useful for taking up specimens from the water or from pickle; common ones will do very well for large objects, but for small objects and parts it is advisable to have one or two sable brushes, as these form a better point.
Some needles fixed in handles will also be necessary. These may be bought, or made by fixing ordinary needles of requisite sizes into the handles sold for small brushes. The needles must be kept free from rust, and should always be carefully wiped after use. A good plan to keep them clean is to stick them in a gallipot in which has been melted a mixture of lard and paraffin in equal proportions.
Small dissecting-knives are useful, but all the work described here may be done with an ordinary pocket-knife in good trim.
Fig. 12.—Three forms of Dipping-tube. Method of using it.
The best preservative for our purpose is formalin, which is sold in a forty per cent. solution. This should be treated as absolute, and a five per cent. solution made. This will really be a two per cent. solution, and is sufficiently strong for general use.
The most profitable use we can make of specimens is to watch their habits while living, and to break them up and learn as much as we can about their structure when they are dead. For us to make a collection of specimens in tubes would be a waste of material.
Fig. 13.—Mounted Needles.