SCIENCE AND. INDUSTRY. 
. The Rat Problem.* 
By THOMAS Eas F.R.C.V.S. 
The brown rat (Mus decumanus), sometimes’ referred t as the 
common brown Hanoverian or sewer rat, is pene than the black rat 
(Mus rattus). 
It is believed to have made its first appearance in this country in the 
year 1729, being brought by ships trading with the East. It has now 
almost superseded’ the black rat, being not only larger, but a more for- 
midable animal. It should be noted, however, that during recent investi- 
gations within the London district, both species have been found living 
in harmony, not only on the same premises, but in. the same rooms. 
Furthermore, on one floor of a factory in Holborn, not only were both 
species of rats captured, but also specimens of the Alexandrine rat—the 
brown variety of the Mus rattus, and the black variety of the Mus 
norvegicus. 
Fecundity—Rats commence breeding when six months old, and are 
fully grown a few months later.’ The period of gestation is about three 
weeks. They may have several litters in the year, each litter comprising 
on an average eight young. They are born naked and blind, are covered 
with hair on the eighth day, and are able to see on the thirteenth day. 
On the twenty-first day they have reached the size of a mouse, and are 
turned out to shift for themselves when about six weeks old. It has 
been calculated that the progeny of a single pair of rats may amount to 
800 in one year. It will be evident, therefore, that rats may increase 
in numbers very rapidly if undisturbed and sufficient food is available. 
Mics breed at six weeks old, and are fully grown at three or four months 
old 
A Menace to Pusric Hearrm, 
Rats may prove to be a real menace to public health in several ways, 
the chief of which are, briefly— 
As carriers and transmitters of dangerous diseases. 
By contaminating food and water supplies. 
By causing insanitary conditions generally. 
Besides the Trypanosoma lewisi, a protozoal parasite which is harm- 
less to its natural host and not known as a parasite of man, the rat is a 
carrier of two other protozoa, namely, Spirocheta icterohemorrhagie 
and Spirochwta morsus muris, which are’ responsible for two serious 
diseases in man, known respectively as— 
Weil’s Disease, or Spirochetal Jaundice; and 
Rat-bite Fever. 
Other diseases that require special consideration. are— 
Plague; 
Trichinosis; and 
Tuberculosis. 
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* Reprinted from The Veterinary Journal. 
288 
