Safe practice in dissection
What this guide is about
The guide is a step-by-step method covering all aspects involved in the delivery of dissection activities
in schools and colleges. The sections being:
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•
•
•
•
Preparing for dissection
Carrying out dissection activities
Clearing away after dissection activities
Disposal of materials from the dissection
Storage of dissection materials and equipment
Relationship to other CLEAPSS documents
The guide gives details of measures that control the risks from sharp instruments and biological agents
of disease (such as microbes and viruses) that occur throughout the preparation, delivery and disposal.
The control measures are summarised in G267: Dissection a starter guide to health and safety.
The details of how to carry out safe procedures for dissection of separate organs or systems in whole
organisms, are found in other CLEAPSS documents, and are summarised in G268: Dissection, a
starter guide to procedures.
Preparing for dissection
Obtaining and preparing the animal materials
Animal materials that have not been preserved
Fresh or frozen animal material should be obtained from premises licensed to sell them for human or
pet consumption, or alternatively from a reputable biological supplier. In these cases, meat inspectors
will have carried out tests to ensure that the products of only healthy animals are released for
consumption. The tests do not remove all possibility of human pathogens being present, so good
hygiene is essential when handling the materials.
During storage, the animal materials should be treated as meat products until the point of use, following
guidelines from the supplier or from government agencies, such as the Food Standards Agency.
In general, the guidelines will advise that animal material should be kept at 50C or below until just
before use. Frozen materials should be thoroughly defrosted in a fridge. Avoid using heat (e.g. from a
microwave) to defrost materials, as this is likely to increase in the populations of microbes.
All non-preserved animal materials should be used within 2 days of purchase or defrosting.
Preserved animal materials
Preserved animal material is often fixed in methanal (formalin) prior to preservation. The methanal will
have been almost completely removed from the specimen during the preservation process, but it is
sensible to ensure that the room is well ventilated during and after the dissection. Nitrile disposable
gloves should be worn when handling the materials.
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Selecting dissection instruments
The above photograph shows the instruments that are most often used in schools.
They have been laid out on a cloth dissection roll.
The instruments are (L-R):
- Sharp/pointed forceps
- Blunt-end forceps
- Point-end dissection scissors
- Point-end mounted needle
- Blunt-end mounted needle
- Scalpel with non-sterile detachable blade
The teacher should select the least hazardous instruments that will allow the activity to
proceed.
The instruments that are usually appropriate for the common dissections are:-
Organs that require opening out (i.e. not lungs etc.)
Heart
-
Blunt- end scissors for cutting through the muscle wall.
Scalpel if fine sectioning of the heart muscle wall is needed
Kidney
Eye
-
Blunt-end forceps for holding the kidney
Point-end (pointed) scissors for making a longitudinal section of the kidney
Egg cup lined with polystyrene for holding the eye
Point-end scissors for cutting into and opening the eye
Whole animal
For opening skin and thorax and abdomen to display organs
- Blunt-end forceps
- Blunt end scissors
For removal of overlying tissue and fat from structures
- Point-end scissors
- Point-end forceps
Where particularly hazardous instruments such as scalpels and pointed forceps/scissors
are being considered, the teacher should trial a range of the instruments available in the
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school before making their final selection.
This is to establish that the instruments are sharp enough to perform the operation.
These pictures show different instruments
being trialled to dissect out celery fibres. The
procedure is very similar to clearing connective
tissue from the digestive tract in mammals.
The trial concluded that blunt-ended forceps
and needles were the most effective and least
hazardous for the process.
Preparing equipment
Dissection instruments
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•
•
All instruments used for dissection activities should be completely free of organic material. See
the section on clearing away for cleaning dissection instruments.
If any instruments appear to be contaminated with organic matter remaining from previous use,
they should be steam sterilised at 121 0 C for 15 minutes before cleaning.
It is usually very difficult to clean very sharp instruments, such as scalpel blades. The re-use of
such instruments therefore needs to be carefully considered.
The blade on the right of this picture was used once (to cut onion
epidermis), then washed and dried.
The picture shows the blade after a period of two weeks.
There is significant corrosion in comparison with the new blade
shown in the left picture.
A corroded blade is more likely to fragment, and more difficult to
remove from the handle.
Microbial contamination of the organic material on the blade may
cause serious infection if the user’s skin is cut during use.
In general, avoid re-using disposable scalpel blades.
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Preparing dissection instruments for carrying around the school
Common sharp dissection instruments
The sharp instruments most often used are:
Sharp pointed forceps
Sharp pointed scissors,
Mounted needles
Scalpels.
Preparing individual sets of instruments for carrying
The instruments should be placed with the
sharp point facing into the compartments of a
dissection roll made from thick cloth.
When the instruments are tied into the
dissection roll, there is no possibility of the
cutting edge or a sharp point moving to cause
an injury.
Preparing class sets of instruments for carrying
Instruments should be placed in rectangular boxes, as described later for storage.
The boxes should be securely lidded and placed in high sided trays.
Preparing surfaces to go under the animal material
If sharp pointed instruments or scalpels are selected, the dissection should take place on a surface
that will absorb any impact with the dissection instrument.
A wooden dissection board is common, but wax trays are sometimes used.
If non-hazardous instruments are selected, a dissecting board / wax tray is not necessary.
Dissection surfaces if non-hazardous instruments are being used
A washing up bowl is useful, as the sides shield
sight of the dissection away from squeamish
students.
In the heart dissection shown here, the waterproof
surface allows water to be measured into heart
compartments, to measure the volume.
The bowl can also be very thoroughly cleaned,
and if necessary disinfected afterwards.
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Dissection surfaces if hazardous instruments are being used
This is a standard dissection board, but any soft wood board (e.g. a wooden chopping board) could
be used.
Contaminated wooden boards are difficult to
clean/disinfect.
A plastic sheet or Clingfilm can be used to prevent
fluids from the dissection penetrating into the
wooden board.
The board/wax tray can be further protected with
several layers of newspaper to absorb any fluids.
Protective aprons/ Lab coats
The use of aprons or lab coats prevents the clothing of dissectors becoming contaminated with fluids
from the dissected animal material. This is necessary, as some items of clothing are laundered
infrequently (e.g. jackets). It is therefore important to ensure that clothing is not contaminated with fluids
from the dissecton, as biological agents may remain active for some time.
The most appropriate protection for clothing is usually a disposable waterproof apron, that will be
discarded immediately after it has been used.
Arranging dissection chambers for containment of hazardous aerosols
If there is a possibility of human pathogens being released into the air during the dissection, there
should be an arrangement for containing any aerosols released from the animal.
The intestine of a non-preserved intact animal is particularly hazardous, as it is likely to contain large
numbers of microbes. The animal should be dissected inside a containment chamber, if there is a
possibility of the intestinal wall being perforated.
Here are some examples of ways to contain aerosols from dissection:
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1. Using a transparent plastic box
An upturned clear plastic box will stop
aerosols reaching the room air.
One end of the plastic box should be cut
away, to allow access for the dissection.
Plastic sheeting placed over the “cut away”
end allows access, and reduces the
possibility of aerosols escaping.
Clearing/disposal:
After the dissection, the box must be
thoroughly disinfected with 1% VirKon, or
70% ethanol.
The disinfected box should be left outside to
ventilate fully.
2. Using a transparent plastic bag
A large transparent plastic bag will contain
aerosols released during dissections of small
animals.
However, the plastic bag may make it difficult
to see a demonstration dissection.
Clearing/disposal: The bag should be
disposed of with the remains of the dissected
animal material.
3. Using a fume cupboard
The picture shows dissection taking place
using a non-vented/portable fume cupboard.
Extra protective plastic could be taped to the
window of the fume cupboard, if considered
necessary. The demonstration dissection can
be clearly seen by the class.
Clearing/disposal:
The fume cupboard must be very thoroughly
disinfected after the dissection.
It may be necessary to change the filters of if
the dissection material is considered to be
particularly hazardous.
As it is not possible to disinfect a vented fume
cupboard fully, they are not suitable for
dissection containment chambers.
TIP
Chambers used to contain aerosols from the dissection also reduce any odours, so the dissection is
much less smelly.
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A lab coat will also protect the clothes, but must be professionally laundered very shortly after it has
been contaminated with fluids from a dissection.
Gloves
As most materials for dissection are food quality, gloves are usually not necessary as thorough hand
washing is effective in removing most of any biological agents, and residues of the dissection from the
hands. Students are generally more likely to wash their hands thoroughly if they have not been wearing
gloves, and are much less likely to touch their face etc. with unwashed hands. However, if the dissector
is unable to wash their hands (e.g. because they are wearing a bandage), then gloves would be
sensible. If the dissector is wearing gloves to protect cuts etc. from microbes, then the gloves used
should bear the number, BSEN 374.
If preserved animal material is to be dissected, the chemicals present on the animal may necessitate
the use of chemically protective gloves. Details of suitable gloves can be found in CLEAPSS
documents . For instance, if methanal (formalin) has been used to fix or preserve the animal, then
disposable nitrile gloves should be used. The suppliers’ safety data sheet should be consulted when
deciding.
Eye Protection
Eye protection is necessary only if there is likely to be a sudden spurt of fluid, and the dissector has to
operate close to the animal material. The most usual case for this will be when an eyeball is being
opened up. Splash resistant spectacles or goggles should be worn (at least BSEN 166).
Safe use of instruments during dissection
It is very important that the teacher clearly shows students how to use dissection instruments safely.
Safe practice in demonstration dissections
• Hold the instruments so that any sharp points
or exposed sharp edges point down into the
dissection board/wax tray. If there is any
slippage when using the instrument, the
point/exposed edge will be absorbed by the
board/wax.
• Always point sharp points or edges away from
yourself, to reduce the possibility of stab
wounds from slippage of pointed instruments,
or cuts from scalpels.
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Safe practice in dissections by students
• Students should be shown how to use
hazardous instruments to carry out the
procedure safely.
• Prior to animal dissections, the teacher may
train students in the use of the instruments, by
dissecting non-hazardous materials (as shown
here).
• The teacher must be vigilant while the students
are carrying out the dissection, to ensure that
they use instruments safely at all times.
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Dissection procedure to reduce the likelihood of perforation of the gut wall
1. Cutting through and clearing the skin
Use blunt forceps to pinch and hold a fold of skin on
the animal’s dissection scissors to make a cut
across the fold.
Close the scissors, and insert the point of the into the
cut made in the skin
Open up the scissors in the cut. This action will free the
skin from the underlying muscle.
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Using the forceps to lift the skin, cut the freed skin
Repeat the clearing and cutting process, working up
and then down the abdomen
Clear the skin away from the entire surface
of the abdomen.
The skin should then either be cut away, or
pinned back onto a dissecting board.
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2. Cutting through the abdominal muscles
Use the same technique as for clearing the
skin, to lift and then cut and clear the
abdominal muscles.
Identify what each structure/tissue is before
cutting.
TIP
If available, sharp pointed scissors are more effective in making the initial cut through the skin or
abdominal wall. For clearing the connective tissues, however, blunt ended scissors are less likely to
cause damage to underlying structures.
3. Identifying the mesenteries and gut regions
Identify the mesenteries- folds of connective
tissue that link the different regions of the
intestines to each other.
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4. Cutting the mesenteries
Using round-end forceps, lift a mesenteric
fold and carefully cut it using very tiny cuts
with sharp pointed scissors.
Continue until all the mesenteric folds
have been cut.
5. Displaying the gut
Use your fingers to carefully spread out
the entire gut onto the dissecting board at
the side of the animal.
The relative length of the different gut
regions can be clearly seen.
TIP
The careful dissection of the gut of a non-preserved animal takes a considerable length of time.
If a teacher wishes to dissect out the gut as a demonstration for a class, it is better to use a preserved
animal, as the process can be carried out much more quickly without there being concerns about
releasing microbes.
Alos note that a non-preserved animal must be disposed of immediately after dissection. A partially
dissected aniaml cannot be stored for a continuation on another day.
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Clearing away and disposal
Safety when cleaning dissection instruments
• Remove and discard scalpel blades into an
appropriate sharps container.
• If instruments are likely to be heavily
contaminated with microbes, sterilise before
cleaning.
• Remove most of the organic material from
instruments by soaking them in a strong
detergent solution (such as that made by
adding dishwasher tablets to water) .Place
the instruments upright with any points, or
sharp edges facing downwards.
• After soaking, use a brush with a handle to
scrub the instruments very thoroughly. It is
important to all remove traces of organic
matter.
• Rinse and dry the instruments thoroughly.
• Take care to avoid cuts when cleaning.
Safe storage of sharp instruments
Instruments should be placed with the all the
hazardous points or edges pointing towards
one end of the container.
The container/drawer should be narrow,
preventing the instruments moving around to
face the opposite direction during storage/
transport.
Large instruments (such as the knives shown
here), should be individually sheathed.
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Placing/replacing scalpel blades
Scalpel blades are designed to cut cleanly through soft materials such as skin. Blades used in schools
are generally non-sterile, so care take care when placing the blade.
NOTE: Used scalpel blades can splinter , wear eye protection when placing or removing them
Placing scalpel blades
Unwrap the blade from its protective
wrapper.
Using the wrapper to protect your hands,
slide the handle onto the bottom of the
blade.
Carefully ease the blade onto the handle.
It is safer to use forceps as shown here.
When the blade is fully in position, it
clicks into place.
Removing scalpel blades
For removing the blade manually, follow the previous instructions for blade placement in reverse
order.
Commercially available scalpel blade removal systems are a safer alternative for removing scalpel
blades. See the following for operation of a system for removing non-sterile blades.
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The blade remover is in the lid of the device,
and the removed blade drops into a sealed
lower container.
Insert the scalpel blade into the slot in the
side of the device, immediately under the lid
.
The blade attachment should be pointing
upwards.
When the scalpel blade is fully inserted, it
should click into place.
Press down firmly on the lid, to release the
blade from the handle.
The scalpel handle can now be pulled free.
The scalpel blade remains in the sealed
lower compartment.
The lower compartment acts as a sharps
container.
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Disposal of used scalpel blades
Scalpel blades that have been used in animal dissections should be placed in a stout sided container,
with no possibility of the blades protruding.
The lid should be secured with tape, and the sharps container should then be wrapped and disposed of
in the normal refuse.
If there is a possibility of large numbers of human pathogens being present (e.g. if the scalpel has
perforated an animal’s gut, or the sharps contain organic material that might have decomposed), the
sharps container should be steam sterilised at 1210C for 15 minutes. The sterilised container should
then be wrapped and placed in the normal refuse.
If the scalpel has cut through a person’s skin, then the blade should be placed in a clinical sharps’
container, and disposed of by a licensed contractor.
Disposal of dissected animal materials
All animal materials should be wrapped in newspaper, and placed in a double layer of bin bags.
The wrapped materials should be placed in a non-recycle bin that is directly handled by the refuse
collectors on the day of refuse collection.
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