Abomasal juice containing rennin was obtained from living calves by means of an abomasal fistula as described by Fomin, in order to ascertain whether the process could be used as an alternative method of manufacturing rennet, should the present curtailed sources fail completely.

The operation for fistula was performed on the calves at the age of about a fortnight by the technique of Phillipson & Innes. The animals received, during the three months for which the experiment lasted, an exclusive diet of whole milk, supplemented by minerals and vitamin D. Although only two calves were used, we feel that the results are nevertheless representative.

Abomasal juice was obtained by allowing them to drink diluted whey and removing it through the fistula after about half an hour. The mean yield of rennin for each ‘perfusion’ from the first calf was 3120 units with a standard deviation of ± 1330. The corresponding figures for the second calf were 5680 and ± 2560 respectively. (One unit of rennin clots 10 ml. of substrate in 100 sec. The substrate is made by dissolving 12 g. spray-dried skim-milk powder in 100 ml. N/50 calcium chloride solution.)