For the preparation of concentrated solutions, only dried calves' stomachs are suitable, and those which have been blown out with air and dried as quickly as possible are best. The small stomachs of the youngest animals are richest in ferment. Fresh stomachs are useless for preparing a concentrated essence, as they yield a thick jelly which, by filtering, gives only a small quantity of liquid. Concentrated extract prepared from stomachs after 14 days is light yellow in colour, whilst that prepared after 6 to 8 months' storage of the stomachs is dark brown. This results from slight decay of the stomach, and as the colour does not affect the usefulness of the product, it is advisable to use stomachs which have been stored for at least 3 months. The portion of the stomach without folds, the portio pylorica,is cut away, as it is poor in ferment.

Acid liquids are usually employed for extracting, as they seem to produce richer solutions, but this is only because they act more quickly at first than water alone. Hydrochloric acid containing 0.1 and 0.2 per cent, of acid in 2 days gave extracts twice as rich in ferment as an aqueous one; but after 8. days all 3 solutions were equally strong. A little thymol was added to prevent decomposition during the experiment. When the temperature is raised to 86°-95° F. (30°-35° C), water acts more rapidly than the acid, and the solution is richer than that produced by acid at the ordinary temperature.

Attempts were made to produce concentrated solutions by means of dilute acids, but without success. A 0.3 per cent, solution of salicylic acid gave a liquid which was quite fresh after 12 months, but after only 2 months its activity had fallen off to the extent of one-half.

A series of experiments made with solutions of common salt containing from 2 to 26 per cent, shows that solutions containing 3 to 6 per cent, of salt yield the liquids richest in ferment, and capable of the highest degree of concentration.

This property of dilute salt solutions depends on the fact, made known by Graham, that common salt is a very easily diffusible substance. Organic acids in combination with common salt are no better extraction agents than the salt alone; 5 per cent, solutions of sodium or potassium sulphate are less efficacious than the same strength of salt solution. Potassium chlorate behaves in much the same manner as common salt; an excess of the potassium chlorate, however, neither acts as efficiently as a precipitating agent nor as a preventive of decomposition.

60 to 80 grm. of calf's stomach, steeped for 5 days in 1 litre of a 5 per cent, solution of common salt at ordinary temperatures, yield a solution of which 1 vol. will coagulate 10,000 vols, of new milk at a temperature of 95° F. (35° C.) in 40 minutes. If the filtered solution is treated with 60 to 90 grm. more of stomach, a dilution of double strength is obtained; another repetition gives a solution 3 times the strength of the original.

To prevent decomposition, about 0*3 per cent, of thymol may be added to the concentrated rennet extract solution. Possibly a slight taste due to this may be detected in the finest cheese, but for the same reason oil of cloves is much more objectionable. Boric acid is on all accounts the best antiseptic to employ, and solutions to which it has been added may be kept in covered vessels for months.

All extract solutions lose strength on keeping; during the first 2 months the solution may become 30 per cent, weaker, then the strength remains nearly constant for 8 months in the case of a solution of 1: 18,000. Alcohol is almost as good an antiseptic as boric acid, if the solution be preserved in well-stoppered flasks.

Detailed experiments show that the time required to coagulate milk is inversely proportional to the strength of the extract solution. From this the strength of a solution can be determined by adding 1 cc. to 1 litre of milk at 95° F. (35° C), and noting the time required to coagulate the milk: this time multiplied by 10 gives the time for the proportion 1: 10,000. (H. Sohxlet.)

Dr. J. Nessler has recently made some experiments with the object of comparing the activity of essence of rennet made according to Sohxlet's method from dried stomachs (as just described) and that of essence made from fresh stomachs. Experiments showed that, using corresponding quantities of dried and fresh stomach, the latter yielded the more active preparation. It was found, moreover, that the activity of the preparation from a fresh stomach could be increased by the removal of mucus, which not only made it more bulky, but prevented it from diffusing the milk so readily, and that this removal could be effected without injury by means of blotting-paper. Preparations made from the top layer of the inside of the stomach, scraped off with a knife, proved much more active than others for which the residue was used, but the residue contained too much ferment to permit it to be left unused. Nessler gives the following instructions for the preparation of an essence of rennet from fresh stomachs: - Chop up a fresh calf's stomach as finely as possible, pour upon it 2 litres water in which 101 grm. common salt have been dissolved, and shake well.

After 12 hours, add 200 cc. of 90° alcohol, and allow the whole to stand, with frequent stirring, in a closed flask for 3 weeks, then decant, and add sufficient Blotting-paper to cover it. After several weeks, during which the vessel must be kept well closed, the essence of rennet is drawn off into bottles and preserved. A liquor prepared in this way was, when fresh, capable of curdling 6000 times its volume of milk, and being kept in a well-corked bottle, it was found, after 2 years, to have diminished its activity only from 1 in 6000 to 1 in 5451. Nessler adds that distilled or rain water gives a more active essence than spring water, and that it is advantageous to mince the stomach as finely as possible. (Pharm. Zeit.)