B 1.0
The field most requisitions leave blank
Four grades, what each one has had done to it, which lesson each one is for, and what the difference costs. This is the half of a specimen order that moves the price most and gets written down least.
Injection is the process of filling an animal's blood vessels with coloured latex after death, so that the vessels can be seen and followed on the tray.
It matters because an uninjected vein is a collapsed grey tube in grey tissue. An experienced demonstrator can find one. Thirty fifteen-year-olds with forty minutes cannot, and a lesson built on tracing circulation in a plain specimen turns into a lesson about how hard it is to see anything.
It also matters because it is labour, and labour is what you are paying for. A plain rat and a double-injected rat are the same rat. The gap between $13.68 and $18.90 is a technician's time, not a better animal.
Which is the whole point of naming the grade on the order: pay for the injection when the lesson uses it, and do not pay for it when the lesson does not.
The convention
- Carmine is arterial
- Red latex, filled from the arterial side. Present from single injection upward.
- Cerulean is venous
- Blue latex, filled from the venous side. Present from double injection upward.
- Yellow is the third system
- The hepatic portal system, filled at triple injection only.
The two colours this website is printed in are the first two of those, which is why a branch of the key is carmine or cerulean and never anything else.
B 2.0 The ladder
Four grades
Named on the order as plain, single, double or triple. Where a species is offered at more than one grade, the entries are different products rather than a discount ladder.
Plain
Pno injection
Fixed and held, nothing filled. The vessels are present, as they are in any animal, but collapsed and the same colour as the tissue around them.
Gross organ anatomy, organ-system identification, external anatomy, skeletal and muscular work, and every lesson where nothing has to be followed through the body. Most school dissection.
Single-injected
Sarteries
The arterial tree filled in carmine. Arteries are thicker-walled and hold their shape, so a single injection gives a clear red map of the supply side.
Lessons about arterial supply specifically, and a reasonable economy where the return side is not part of the exercise.
Double-injected
Darteries + veins
Arteries in carmine, veins in cerulean. This is the grade most circulation labs actually need, because the point of a circulation lesson is that it is a circuit, and a circuit needs both halves visible.
Heart and vessel work, tracing a circuit from heart to periphery and back, comparative anatomy, and anything where students have to distinguish supply from return.
Triple-injected
T+ hepatic portal
Arteries, veins, and the hepatic portal system in yellow — the vessels carrying blood from the gut to the liver, which is the part of the circulation students find least intuitive.
Portal circulation specifically, digestive-plus-circulatory sequences, and most college-level comparative anatomy. Usually more than a school lesson needs.
B 3.0 What it costs
The same animal, at each grade
The clearest way to see what injection costs is to hold the species still and change only the grade.
| Species | Plain | Single | Double | Triple |
|---|---|---|---|---|
| Frog Rana pipiens, 3–4″ | $5.20 | $7.10 | $8.95 | $12.40 |
| Rat Rattus norvegicus, 8–9″ | $13.68 | $16.20 | $18.90 | $24.50 |
| Fetal pig Sus scrofa, 10–12″ | $14.80 | $17.40 | $19.80 | $26.00 |
| Cat Felis catus, 14–17″ | $46.00 | $62.00 | $78.00 | $95.00 |
The rat, plain, at $13.68 each is a current published unit price. Notice that the step from plain to double is between 40% and 70% depending on the species — which is worth knowing before a budget is written, and is the reason this field belongs on the requisition.
Catalogue prices are USD per unit at the pack size stated, exclude shipping, handling, hazardous-materials surcharges and any applicable tax, and are catalogue ranges for planning a requisition rather than an offer or a quotation. Reviewed September 2026. A figure for your order is confirmed on a written quotation. See the disclaimer.
B 4.0 Choosing
One question decides it
Does anything in this lesson have to be followed?
If a student has to start at one place and trace a path to another — heart to limb, gut to liver, gill to body — then that path has to be visible, and you need it injected. If the student has to find, name and describe things that sit in one place, plain is correct.
That is genuinely the whole test, and it is more reliable than working from the grade level of the class. A middle-school lesson that traces circulation needs injection; a college lesson on organ identification does not.
If the answer is yes and you are not sure how far to go: double. Single is a narrow economy that only makes sense when you have decided the return side is out of scope, and triple is for portal circulation specifically.
Common mistakes
- Buying plain for a circulation lab
- The most expensive mistake on this page, because the lesson does not work and the money is spent either way.
- Buying triple for a school lab
- Paying for a third system that the syllabus does not mention, on every specimen.
- Leaving the field blank
- Somebody else chooses, reasonably, and you find out on the morning of the lab.
- Assuming last year's order was right
- Repeat orders inherit whatever grade the first one happened to get, including the wrong one.
Describe the lesson and we will name the grade
You do not have to arrive at this decision alone. Tell us what students have to be able to do by the end of the session and we will tell you which grade does it, including when the answer is the cheaper one.
Niles Biological, Inc. · 9298 Elder Creek Rd, Sacramento, CA 95829