Weighing: use of laboratory balances

Balances may be either electrically or manually operated. All types should be posi- tioned on a firm level bench away from vibrations, draughts and direct sunlight. 

The balance is used to weigh chemicals for production of reagents, and cleanliness is essential if accurate results are to be obtained: 

● Remove dust by blowing or using a soft brush. 

● Remove stains or chemicals using a soft brush. 

● Use a plastic weigh boat or filter-paper to weigh chemicals on the balance; never place chemicals directly on to the pan.

Important: If water has been used to clean the balance, make sure that it is thoroughly dry before weighing. Always set the balance to zero before weighing. Check the accuracy of the balance regularly according to the manufacturer’s recommen- dations. Handle loose weights with forceps. 

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Use of a microscope in laboratory

The microscope is an essential instrument for the diagnosis of disease. It is a preci- sion instrument and requires careful maintenance to prevent damage to the me- chanical and ocular parts and also to stop fungi from obscuring the lenses. 

1. Components of a microscope 

The various components of the microscope can be classified into four systems: 

— the support system 

— the magnification system 

— the illumination system 

— the adjustment system. 

Support system (Fig. 3.1) 

This consists of: 

— the foot (1) 

— the limb (2) 

— the revolving nosepiece (objective changer) (3) 

— the stage (4) 

— the mechanical stage (5), which gives a slow con- trolled movement to the object slide. 

Magnification system (Fig. 3.2) 

This consists of a system of lenses. The lenses of the microscope are mounted in two groups, one at each end of the long tube — the body tube. 

● The first group of lenses is at the bottom of the tube, just above the preparation under examination (the object), and is called the objective. 

● The second group of lenses is at the top of the tube and is called the eyepiece. 

Objectives

Magnification

The magnifying power of each objective is shown by a figure engraved on the sleeve of the lens (Fig. 3.3):

— the x 10 objective magnifies 10 times;

— the x 40 objective magnifies 40 times;

— the x 100 objective magnifies 100 times.

Fig. 3.1 Components of the support system of a microscope
1: foot; 2: limb; 3: revolving nosepiece; 4: stage;
5: mechanical stage.

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Equipments for laboratory use

The following is a list of the apparatus needed to equip a laboratory capable of carrying out all the examinations described in this manual. Such a laboratory would usually be located in a small rural hospital (district level) which might have be- tween 60 and 100 beds.

1. Essential laboratory instruments

Microscopes

The laboratory should be equipped with two microscopes.

● One microscope is for use in haematology. It should have an inclined binocular tube, a mechanical stage, three objectives (x 10, x 40, x 100), two eyepieces (x 5,x 10), a condenser and an electric lamp that can be connected to the mains electricity supply or a battery.

● The second microscope is for use in other laboratory procedures (parasitology, urine analysis, bacteriology, etc.) and should have an inclined binocular tube and accessories as listed above.

At the health centre level one binocular microscope is sufficient.

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Water for laboratory use

The medical laboratory needs an adequate water supply for its work. It requires: 

— clean water 

— distilled water 

— demineralized water (if possible) 

— buffered water (if possible). 

1. Clean water 

To check whether the water supply is clean, fill a bottle with water and let it stand for 3 hours. Examine the bottom of the bottle. If there is a deposit, the water needs to be filtered. 

Filtering

Using a porous unglazed porcelain or sintered glass filter

This type of filter can be attached to a tap. Alternatively, it can be kept immersed in a container of the water to be filtered (Fig.2.28).

Important: Filters of this type must be dismantled once a month and washed in boiling filtered water.

Fig. 2.28 Filtering water using  a porous unglazed porcelain or sintered glass  filter

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Plumbing: simple procedures in laboratory

A fault in the plumbing of the laboratory (a dripping tap, a blocked sink, etc.) can hamper laboratory work considerably. Some simple remedies are described below, in case a plumber is not readily available.

Fig. 2.15 Tools and materials for plumbing repairs

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Electricity in laboratory

A reliable energy supply should be available to ensure continuity of the work in a laboratory. The energy can be provided from the following sources:

— mains electricity supply

— generators

— solar energy supply system.

Remote laboratories often have problems in ensuring a continuous supply of elec- trical power and may need to generate electricity by using a local generator or a solar energy supply system.

1. Sources of electricity

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Plan of a peripheral medical laboratory

1. A one-room laboratory

Figure 2.1 sets out the possible arrangement of a peripheral medical laboratory attached to a health centre. It shows a laboratory suitable for carrying out some or all of the techniques described in the manual. The plan is limited to one room, since often this is all the space that is available for the laboratory. The room should measure at least 5 m ¥6m.

Figure 2.2 indicates another possible arrangement of a peripheral laboratory. It can obviously be modified to suit different circumstances.

Fig. 2.1 Plan for a one-room laboratory

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