Last month, I examined the issue of ‘curdled milk in the breast’ in Greek and Roman medicine. The texts I quoted all used the words ‘cheesy’ (turōdēs) or ‘to make cheesy’ (turoō) – they did not refer to rennet (putia), the curdling agent in cheese making. This month, I look into the role of rennet in ancient medicine, and particularly in ancient embryology and gynaecology. Rennet is a liquid found in the stomach of young mammals; it helps sucklings digest their mother’s milk. Used in cheese making, it causes milk to separate into curds (solid element) and whey (liquid element). In a well-known passage, Aristotle (fourth century BCE) compared the action of semen in generation to that of rennet in cheese making:
The action of the semen of the male in ‘setting’ the female’s secretion in the uterus is similar to that of rennet upon milk. Rennet is milk which contains vital heat, as semen does, and this integrates the homogeneous substance and makes it ‘set’. As the nature of milk and the menstrual fluid is one and the same, the action of the semen upon the substance of the menstrual fluid is the same as that of rennet upon milk (Generation of Animals 739b21-27. Translation: A.L. Peck).
Scholars have found similar analogies between generation and cheese-making in various cultures: semen is like rennet; women’s blood is like milk; children are like cheese. In this context, it is interesting to note that actual rennet was used in ancient medicine either to help or to hinder conception, as well as for various other purposes. The pharmacological writer Dioscorides (first century CE) writes:
A weight of three oboloi of hare’s rennet taken with wine is suitable for those bitten by wild animals, for dysenterics, for women who suffer from discharges, for blood clots, and for coughing up blood from the chest; applied to the cervix with butter after menstruation, it aids conception, but if drunk after menstruation, it causes barrenees… (Dioscorides, De materia medica 2.75. Translation: L. Beck)
The reader can be forgiven for not immediately seeing the linking factor between these conditions. After several paragraphs, Dioscorides provides the key: rennet, he says ‘congeals substances that have been dissolved and dissolves substances that have been congealed’. Rennet dissolved clots of blood; in the case of bloody sputa and female discharge, it must have either liquefied that blood, enabling its elimination, or ‘curdled’ it; applied in a pessary, it facilitated the role of semen in ‘curdling’ the menstrual blood; but drunk after menstruation, it probably ‘dissolved’ any ‘curdled’ blood in the womb, that is, it caused what we would an early abortion; in dysentery it may have ‘curdled’ faeces in the intestine. What about the role of rennet in the treatment of bites? Bites were thought to cause blood clotting, hence the recommendation to use rennet.
After discussing hare’s rennet, Dioscorides turns to seal’s rennet, explaining that it is particularly good in cases of epilepsy and uterine suffocation, that is, the feeling of suffocation that accompanies movements of the womb. Both ailments were conceived as forms of ‘suffocation’ (pigmos). The rationale for the use of rennet might have gone something like this: suffocation is caused by a ‘choking’ agent; rennet can dissolve what is congealed; rennet will dissolve the choking agent in uterine and epileptic suffocation. Interestingly, seal’s rennet is the only rennet mentioned in the Hippocratic Corpus (a series of texts written in the fifth and fourth centuries BCE), where the following recipe is recommended for the treatment of uterine suffocation:
If the womb leans and lies against the groin: the skin of seal’s rennet, sponge and bryon (possibly a sea-weed); chope them fine; mix together with seal oil; and fumigate. (Hippocratic Corpus, Diseases of Women 2.203).
Theophrastus, in his Enquiry into Plants (late fourth century BCE), informs us that the all-heal of Heracles, mixed with seal rennet, helps in epilepsy (9.11.3).
Why seal’s rennet? Surely it would have been simpler to get the rennet from a hare or a calf? Well, seals were seen as liminal animals in the ancient world: they breast-fed their cubs, yet looked like fish; they lived both on land and in water. Their rennet – and Dioscorides says that one must use the rennet of a cub who cannot yet swim – must therefore have been thought valuable in the treatment of diseases that themselves involved ‘liminal’ states: the ‘near-death’ condition that characterizes epileptic seizures and other forms of suffocation.
 See in particular Ott, Sandra. “Aristotle among the Basques: the’cheese analogy’of conception.” Man (1979): 699-711.