Rattus norvegicus: the lab rat

The albino Rattus norvegicus used in laboratories (photo above by Sarah Fleming) goes back to the Wistar Institute in Philadelphia. Physiologist Henry H. Donaldson took four pairs of albino rat with him when he joined the Institute in 1906, and work there by Donaldson, Helen Dean King, and others resulted in the development of a standardised “Wistar rat.”

In his 480-page tome The Rat: Data and reference tables for the albino rat (Mus norvegius albinus) and the Norway rat (Mus norvegius) of 1915 (revised in 1924), Donaldson notes: “In enumerating the qualifications of the rat as a laboratory animal, and in pointing out some of its similarities to man, it is not intended to convey the notion that the rat is a bewitched prince or that man is an overgrown rat, but merely to emphasize the accepted view that the similarities between mammals having the same food habits tend to be close, and that in some instances at least, by the use of equivalent ages, the results obtained with one form can be very precisely transferred to the other.

What Donaldson means by the latter point is: “If the life span of three years in the rat is taken as equivalent to 90 years in man, it is found that the growth changes in the nervous system occur within the same fraction of the life span (i.e., at the equivalent ages) in the two forms.

Since Rattus norvegicus has adapted to live with people (e.g. in tunnels under our cities), it makes for a perfect laboratory animal. Running rats through mazes of varying kinds has become an established way of studying learning, as in this video from the San Diego News Network:

Chromatic polynomials

Network colouring is an fascinating branch of mathematics, originally motivated by the four colour map theorem (first conjectured in 1852, but proved only in 1976). Network colouring has applications to register allocation in computers.

For each network there is a chromatic polynomial which gives the number of ways in which the network can be coloured with x colours (subject to the restriction that directly linked nodes have different colours). For example, this linear network can be coloured in two ways using x = 2 colours:

The corresponding chromatic polynomial is x (x − 1)3, which is plotted below. Zeros at x = 0 and x = 1 indicate that at least 2 colours are required.

For the Petersen network below, the chromatic polynomial is:

x (x − 1) (x − 2) (x7 − 12 x6 + 67 x5 − 230 x4 + 529 x3 − 814 x2 + 775 x − 352)

This polynomial has zeros at 0, 1, 2, and 2.2051, and is plotted below:

Chromatic polynomials provide an interesting link between elementary and advanced mathematics, as well as an interesting case study of network algorithms.

Circulation: William Harvey’s Revolutionary Idea (a review)

Circulation by Thomas Wright

I recently read Circulation: William Harvey’s Revolutionary Idea by Thomas Wright. This interesting biography of William Harvey concentrates on his discovery of the circulation of the blood through the body, and his publication of Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus in 1628. The historical and social context of Harvey’s work is described particularly well.

William Harvey

Harvey’s idea had the potential to revolutionise medicine, doing for biology what Galileo had done for astronomy. Sadly, although Harvey’s work undermined the basis for pointless treatments like bloodletting, the respect accorded to ancient Greek medicine kept such treatments alive for centuries after they should have ceased.

An illustration from Harvey’s book

This well-written book is well worth reading, and of interest to students of science, history, and medicine (although the descriptions of live dogs being dissected are a little disconcerting). It won the 2012 Wellcome Trust Book Prize.

Circulation by Thomas Wright: 3.5 stars