49 
PRESIDENTIAL ADDRESS. 
the absence or diminution of these controlling factors, the 
rate of increase may be very rapid, in fact, in the absence 
of all inhibiting circumstances, astounding. 
The following table (Table I.) shows the number of rat 
foetuses found on examination in the Microbiological La- 
boratory of the Department of Public Health, in the three 
species, H. rattus, EL. norvegicus, and M. musculus, during 
the three years 1915, 1916, 1917. As not infrequently, 
when pregnancy is well advanced, one or two partly ab- 
sorbed fcetuses may be found in the horns of the uterus, the 
number born per litter will be somewhat less. Still, for 
practical purposes, these figures may be taken as showing 
the number actually born. 
Bere I.—Number of Fetuses found in Rats and Mice in Sydney 
during the Years 1915, 1916 and 1917. 
Epimys rattus. Epimys norvegicus. Mus musculus. 
Habis | Nomar of Apnrosinete|Orbuck | approximate) much [Approniont 
per litter. pregnancies | population - Bee population. fee population. 
] 4 4 ] 1 2 2 
Z 6 12 0 0 il 2 
3 34 102 4 12 5 15 
4 43 172 5 20 9 36 
5 1936 680 35 175 8 40 
6 145 870 M7 102 5 30 
rs 160 1120 4] 287 5 30 
8 7 ; 616 30 240 2 16 
9 72 648 49 441 1 9 
10 4] 410 22 220 0 0) 
ll 14 154 16 176 0 0 
|e 8 96 9 108 0 0 
13 1 13 6 78 0 0 
14 3 42 4 56 0 0 
15 0 0 0 0 0 0 
16 0 0 0 0) 0 0 
17 l en 0 0 0 0 
18 0 0 1 18 0 0 
Total 745 4966 240 1934 38 185 
Average per litter 6°66 8:05 4°87 
D—May 1, 1918. 
