Calculating An Animal's Blood-Volume Without Killing It
By Enrico Uva | July 17th 2011 11:43 AM | 4 comments | Print | E-mail | Track Comments

I majored in chemistry, worked briefly in the food industry and at Fisheries and Oceans. I then obtained a degree in education. Since then I have...

View Enrico's Profile
There are many reasons why camels can survive the desert’s arid conditions:
1. Instead of wasting water while excreting urea, their bodies recycle part of it. The nitrogen can be used to make amino acids, the building blocks of protein.
2. Although they are warm-blooded, they still adjust their body temperature to the environment from about 37 to 40oC.
3. Their fat is concentrated in their hump(s), so they have less insulation throughout the rest of the body. A camel does not store water in its hump(s) or in its stomach.
4. Whereas the blood of most water-deprived mammals becomes thicker, leading to poor circulation and dangerously high body temperatures, a camel’s blood vessels retain most of their water. How was this discovered?

In the 1950’s, Knut Schmidt-Nielsen and his wife injected a harmless dye in to a camel’s bloodstream. They waited a while for the dye to distribute itself evenly. Then they took a blood sample and measured the concentration of the dye. Then the camel went 8 days without drinking in the desert heat. Although it lost a lot of weight (over 40 litres of water), the concentration of the dye in the blood revealed that the blood had only lost about 1 litre of water. In other words the rest of the water had been lost from tissues.

This is the kind of calculation that the Nielsens used:

Suppose that the original concentration of the dye had been 4.95 mg/L in 100 L* of blood. If the concentration of the dye had then increased to 5.00 mg/L, using C1V1 = C2V2,

4.95(100) = 5.00V2, would reveal V2 to be 99 L, a change of only 1 L.

But how did they know that the camel had a 100L of blood without killing it ? Let's say they had originally injected 8.0 mL of 6.19 g/L of dye. After even distribution of the dye(before the camel went 8 days without drinking), the concentration became diluted to 0.000495 g/L, then
C1V1 = C2V2,

(0.0080)(6.19) = 0.000495(0.008+V2), would reveal V2 to be about 100 L.

where

V
is the volume of the camel's blood.

Knut Schmidt-Nielsen who passed away three years ago(2008) wrote at the beginning of his memoirs:
"I has been said that schools impart enough facts to make children stop asking questions. Those with whom the schools don't succeed become scientists."

Reference:

Scientific American. The Physiology of the Camel. December, 1959.

Picture from George Holton, The National Audubon Society Collection/Photo Researchers

That is some dye that stays 8 days inside the bloodstream, doesn't get fat or plasma bound, ...
I suspect a large margin of error here.
I suspect a large margin of error here.
Possibly. I wanted to look at his original paper to find out the exact nature of what was injected, but I could not get hold of it. if you have access to any of his work, please forward his publications to me(other than Scientific American summary), so I could do a proper follow-up.
Thanks Hank.

Here's the relevant part:

To better address Sascha's questions, the dye is T 1824, which is Evans Blue, a diazo compound that's been used in blood-volume studies since 1915.

The dye combines firmly with plasma albumin when injected into the blood stream and which leaves the circulation very slowly. The dye is removed from the vascular system principally by diffusion into the extra vascular tissues while still bound to albumin. It is also taken up in small amounts in the bile and by wandering phagocytic cells.

Numerous papers have been published on methodology and we supply the latest computer technique, a programme for blood volume determination using EB and multiple sample technique. Knowing the amount of dye injected, times of blood sample collections, and spectrophotometer readings for the samples, the program (1) automatically corrects each sample for its own blank value, (2) finds the best EB disappearance curve, (3) back-calculates to injection time, (4) corrects for preceding dye concentration and if the hematocrit is known, (5) returns the plasma volume.
http://www.evansblue.co.uk/

A similar experiment was done with donkeys 20 years after, and the error was close to 10%. (source:
jap.physiology.org/content/39/3/496.full.pdf) But I imagine that the latest techniques are more accurate.
So you're right Sascha, the error was a bit on the large side.