Respiratory rates ( f ) of cotton rats infected with A/Wuhan/359/95. The arithmetic means of f in infant cotton rats (open circles) are shown and compared to adult cotton rats (closed diamonds) on days 0 (before infection), 1, 2, 3, 4, 5 and 7 p.i. Four to ten animals were used in each group. The SEM is shown for each group. Means that were significantly different from f measured on day 0 (t test within in each age group, p < 0.05) are indicated with an * for adults and ❊ for infants.