More recently Gould and Pyle (_Anomalies and Curiosities of Medicine_, p. 80) have briefly summarized some of the ancient and modern records concerning the longings of pregnant women. Various theories are put forward concerning the causation of the longings of pregnant women, but none of these seems to furnish by itself a complete and adequate explanation of all cases. Thus it is said that the craving is the expression of a natural instinct, the system of the pregnant woman really requiring the food she longs for. It is quite probable that this is so in many cases, but it is obviously not so in the majority of cases, even when we confine ourselves to the longings for fairly natural foods, while we know so little of the special needs of the organism during pregnancy that the theory in any case is insusceptible of clear demonstration. Allied to this theory is the explanation that the longings are for things that counteract the tendency to nausea and sickness. Giles, however, in his valuable statistical study of the longings of a series of 300 pregnant women, has shown that the percentage of women with longings is exactly the same (33 per cent.) among women who had suffered at some time during pregnancy from sickness as among the women who had not so suffered. Moreover, Giles found that the period of sickness frequently bore no relation to the time when there were cravings, and the patient often had cravings after the sickness had ceased. According to another theory these longings are mainly a matter of auto-suggestion. The pregnant woman has received the tradition of such longings, persuades herself that she has such a longing, and then becomes convinced that, according to a popular belief, it will be bad for the child if the longing is not gratified. Giles considers that this process of auto-suggestion takes place "in a certain number, perhaps even in the majority of cases."[184]