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[N. 8. Vol. XL VII. No. 1224 

tion of the magnesium sulphate is completed 
by washing the crystals with very dilute al- 
cohol, after which they may be immediately 
used for further precipitation. 

In the complete paper the authors will dis- 
cuss in some detail the application of this 
method to the quantitative determination of 
pectin in the laboratory or in commercial jelly- 
making establishments. It is considered es- 
pecially desirable at this time to point out that 
precipitation by magnesium sulphate may ad- 
vantageously supplant the use of alcohol in 
the household test for pectin. "While alcohol 
is not ordinarily available to the housewife, 
Epsom salts are to be found in every home and 
in almost every grocery store. By heating a 
small quantity of the aqueous extract of fruit, 
dissolving Epsom salts therein, and observing 
the amount of pectin thrown out of solution, 
one obtains an accurate measure of the pectin 
content of the fruit and is thereby enabled to 
form a judgment as to the amount of sugar 
necessary to form a jelly. 

Discussion of many details of technique and 
of certain applications of the method here 
presented in outline are necessarily reserved 
for presentation in the full paper immediately 
forthcoming in the journal already named. 
C. A. Magoon, 
Joseph S. Caldwell 

Office Horticultural and 
Pomologioal Investigation, 
Bureau of Plant Industry, 
Washington, D. C. 


At this time when the government is using 
great numbers of albino rats and mice for 
inoculation purposes, numerous letters have 
been received from various sources asking for 
information regarding a source of supply and 
the care and breeding of these animals. This 
demand is so widespread that it is deemed 
most expedient to give this information in a 
simple form and to disseminate it to the 
greatest number of people by publishing it in 
this journal. In so doing those persons who 
are anxious to do their bit in this present 
crisis and who reside sufficiently near base 

hospitals and cantonments may be able to rear 
and supply these animals. 

Albino rats and mice are exceedingly easy 
to raise. Their care and feed are practically 
the same and the cages in which they are kept 
can be identical. The cages for mice can, 
however, be much smaller. Our colony at the 
present time consists wholly of rats and the 
following applies strictly to them. It in gen- 
eral applies to mice also. These animals can 
ordinarily be handled by the bare hands with- 
out any danger of being bitten. Occasionally, 
however, a mother with young may be less 
docile if her young are disturbed. In such 
cases the use of a pair of heavy gloves is ad- 
visable. The oftener the rats are handled and 
petted the less likely they are to bite. 

The cages in which our rats are kept and 
which we have found most satisfactory are 
made of one-fourth-inch galvanized wire net- 
ting with all the comers, edges and doors 
bound, or reenforced by galvanized iron (Fig. 
1). They are made 12 inches high, 18 inches 
wide and 24 inches long. A partition of 
woven galvanized wire, provided with a sliding 
door (D4in. X^in.), divides this into two 
compartments 12 in. X 12 in. X 18 i n - Each of 
these compartments is provided with a woven 
wire door (D, 6 in. X 6 in.) which slides up in 
runners made of galvanized iron (Rn). These 
doors are of ample dimensions to enable one to 
easily reach into all parts of the cage. 

The bottom is separate and composed of 
galvanized iron 20 in. X 25 in. with three of 
the sides turned up 1 in. The front side is 
left flat to facilitate cleaning. The cage thus 
sits in this bottom and can be readily lifted off 
when cleaned. This process, which should be 
attended to at least once in two weeks, can be 
accomplished without handling the rats or 
without danger of their leaving the compart- 
ments to which they belong. This is done by 
placing the whole cage on a broad table, lifting 
the top about one half an inch and carrying it 
along to the bare table. The rats are thus 
forced along with the cage and the bottom left 
free. The old sawdust and excelsior used for 
bedding are now scraped out and a fresh sup- 
ply added. The cage containing the rats in 

June 14, 1918] 



their proper compartments is now replaced in 
the same manner that it was removed. 

Clean fresh water is constantly supplied by 
means of- an inverted bottle (B) provided with 
an air-tight rubber st6pper (R) and glass tube 
5 mm. in diameter ((■?). The spring clips (0) 
permit ready removal of the bottles for filling. 
The bottles are supported at the lower end on 
two bent wire nails (8) between which the 
glass tube passes (Figs. 1 and 3). We have 
found bottles containing eight ounces the most 

serviceable, as they are not too large and do 
not need refilling very often. 

The albino rat is omnivorous in its diet and 
will devour almost anything a man will eat. 
They should be fed once each day. The food 
consists of cracked corn daily, such table 
scraps as are available, green stuff, such as 
lettuce, cabbage, etc. Where a large number 
of rats are being reared it is advisable to 
procure the refuse from a restaurant or hotel. 
Table scraps give a fairly balanced diet and 




6'x6 " 


Fig. 1. Perspective drawing of the woven- wire partition dividing the two compartments; D 6 in. 

portion of the cage showing the dimensions and , x 6 in., sliding doors into cages; G, glass drinking 

plan of construction. tube from water-bottle; L, lifts for sliding doors; 

B, drinking bottle; C, spring clips for holding B > rubber ^PP^ Sn > galvanized-iron runs for 

bottle; Cg, cage; D 4 in. X 4 in., sliding door in slidin g doors 5 S > supports for bottle. 

Fig. 2. Galvanized iron bottom, giving dimensions showing the support of the bottle, 8, and the man- 
and plan of construction. ner in which the tube leads into the eage. 

Fig. 3. Sectional view of drinking fountain 



[N. S. Vol. XLVII. No. 1224 

we have had excellent success with this food. 
If table scraps are not available, cooked beans. 
nuts and meat two or three times per week 
should be provided. The amount of food 
given should always be greater than will be 
consumed if one is desirous of quick returns. 
When rats are fed on a sufficient quantity of a 
well-balanced ration they are very prolific and 
grow rapidly. 

A pair should be placed in each compart- 
ment. The female comes in heat about every 
five days and the period of gestation is ap- 
proximately 21 days. The period of gestation 
is prolonged a few days if the female is nurs- 
ing a litter of young during this time. Nu- 
merous instances are on record where mating 
has occurred the same day that young were 

The number of young in a litter varies from 
one to fifteen, the average number being about 
six or eight. They grow rapidly and can be 
weaned at 30 or 35 days of age. If one de- 
sires to maintain a pure breed the young 
should never be allowed to remain with the 
parents after they have reached the age of 
fifty days, as breeding is likely to occur. A 
litter should always be weaned regardless of 
age as soon as (preferably just before) a new 
litter is born to prevent starvation of the new- 
born. In case the weaned litter is very young 
(25 to 35 days) milk should be added to their 
diet. To prevent inbreeding the sexes should 
be separated at weaning and confined in sepa- 
rate cages. With proper food, however, in- 
breeding can go on without apparent detriment 
for a number of generations. 

The sexes in the young may be distinguished 
by the following characteristics: 

The males may be recognized by a greater 
distance between the anus and the genital 

In the male the genital papilla is larger 
than in the female. 

At about 15 days of age the nipples are 
visible in the female. 

After the hair covers the body a strip ex- 
tending from the anus to the genital papilla 
remains almost bare in the female, while in the 
male this region is covered with hair except a 

small area immediately below the anus which 
later becomes the scrotum. 

After the descent of the testes into the 
scrotum the males can readily be distin- 

The age at which the young females become 
sexually mature varies between rather wide 
limits, but usually between 70 and 90 days. 
The earliest age at which we have found them 
sexually mature is 69 days. Lantz 1 records 
a case of sexual maturity at the early age 
of 35 days and Jackson 2 one at 49 days. Sexual 
activity in the females may continue until 
they have reached the age of 600 days. We 
have not determined the ages at which sexual 
activity begins and ceases in the male. 

A great difference is noticed in the ability 
of females to produce young. Some appear to 
be sterile, while others have given birth to as 
many as nine litters. If one is desirous of 
securing numbers, the offspring from prolific 
breeders should be selected for breeding. 

The rats do best in a well-ventilated room 
of fairly uniform temperature. Extreme tem- 
perature should be avoided. 

Since these animals need daily attention 
they can not be shipped long distances unless 
provision is made for watering and feeding 
them en route. Our available supply is quite 
limited but we can generally furnish a few 
pairs to any one within shipping distance who 
is willing and able to breed rats for purposes 
of supplying the government, or for general 
scientific research. 

The three main items for success are clean- 
liness, a sufficient quantity of a balanced 
ration, and avoidance of great changes in 
temperature. With these carefully looked 
after success is assured. 

J. E. Slonakek 
Physiological Laboratoeies of 
Stanford University 

i David E. Lantz, ' ' Natural History of the Eat, ' ' 
In "The Eat and its Eelation to the Public 
Health," by various authors. P. H. and M. H. 
Service, Washington, 1910. 

2 C. M. Jackson, ' ' On the Eeeognition of Sex 
through External Characters in the Young Eat," 
Biological Bulletin, Vol. XXIII., No. 3, August,