PEArEET NO} 253 
U. S. DEPARTMENT OF AGRICULTURE 
Raising Laboratory Mice and Rats 
By ORSON EATON, animal husbandman, and CuHaRLES A. CABELL, assistant 
chemist, Bureau of Animal Industry, Agricultural Research Administration 
INTRODUCTION 
The mouse is probably one of the most widely distributed animals in the 
world. It has world-wide distribution, having followed man to all of his 
environments. The mouse probably originated in central Asia, spread to 
other portions of Asia and to northern Africa, then to central and northern 
Europe. The mouse came to Mexico and South America on the ships of the 
southern European explorers, and to the United States and Canada from 
northern and central Europe with the early colonists. 
The mouse was known to the Aryan tribes of Asia 4000 B. C. Pottery de- 
picting mice has been found in Egypt dating back to 2000 B. C. A cult in 
Asia Minor, northern Africa, Greece, and some of the neighboring islands 
worshiped the mouse for nearly 3,000 years. Mice were raised in the temples 
to be used in connection with worship. The mouse was depicted on many 
ancient coins. The mouse is not native to Japan, but stories of it exist in 
Japanese folklore. Chinese priests made use of the mouse for many centuries. 
During the nineteenth century European zoologists bred mice for use in the 
study of inheritance of color varieties. ‘Their results remained uninterpreted 
until after the rediscovery of Mendel’s laws in 1900. 
Production of the albino rat has become a subject of wide interest, prin- 
cipally on account of its many virtues as a laboratory animal. Experimental 
techniques involving the use of these animals have been employed for many 
years, but extensive use of the rat began with modern scientific methods of 
investigation. Experiments with vitamins, hormones, and foods and drugs 
concerned with animal and human well-being and growth require large num- 
bers of these animals. 
The wild gray rat can be tamed and handled, and is sometimes used for 
special laboratory work. However, various strains of albino and piebald mu- 
tants which are more docile and less easily frightened by strange sounds and 
movements are being produced more extensively for experimental and teach- 
ing purpose:. 
DESCRIPTION 
Two species of mice of the family Muridae have been domesticated: Mus 
musculus and M. bactrianus. The former is the larger of the two species, has 
a longer tail, and differs in skull proportions from the latter. The belly is 
gray. WM. bactrianus has fewer young per litter and has a white belly. The 
two species cross readily and the offspring are fertile. 
The white rat (Mus norvegicus albinus) is a member of the subfamily Mur- 
inae of rodents. The genus Mus, including rats and mice, contains about 
130 species. They are all exclusively of Old World origin. ‘Two species of 
rats have migrated to the United States in large numbers from Europe. First 
came the black house rat (M. rattus), which has been supplanted largel by 
the brown or Norway rat (M. norvegicus). This latter species now is found 
Issued May 1949 
834082°—49 
