Table 3. Effect of medium pH on laterality of Xenopus embryos.

pH of medium	Sample size (n)	Heterotaxic	χ2	P
7.8 (control)	334	1%	–	–
4	129	19%	46.6	≪0.001
5	108	6%	7.3	0.007
6	122	6%	6.0	0.014
7	110	0%	0.3	0.568
8	152	0%	0.7	0.416
9	106	0%	0.3	0.586
10	101	1%	0.1	0.718
11	95	4%	2.2	0.137

Embryos were kept in 0.1 × MMR at different pHs (column 1) from the one-cell stage to stage 12-13, then scored for organ position at stage 45. At pH 7 or above, embryos were no different from controls. At pH 6 and 5, the incidence of heterotaxia increased to low but significant levels. At pH 4, 19% of embryos were heterotaxic.