“…Venn (1944) found variations from 5 to 11 in 2 litters at the age of 5 to 17 days. Frazer (1938) made 31 observations at different times within the first 2 weeks, the counts ranging from 5 to 27, and Schalm (1961) found variations from 5.6 to 19.1 in a litter of 9 during the first 10 days after birth.…”