This is the flocculent, frothy, semiliquid substance, generated during the fermentation of saccharine liquids. For use it is obtained chiefly from brewers, being largely produced in the preparation of malt liquors.

It has a sour and vinous odour, and bitter taste. in composition it is exceedingly complex; but it always contains a considerable proportion of gluten, and, when examined by the microscope, is seen to abound in the sporules of a fungous plant, which is supposed to play an essential part in the fermenting process. For a more particular account of it, see the U. S. Dispensatory. Here it is considered mainly in reference to its property of exciting fermentation in starchy and saccharine liquids, converting starch into sugar, this into alcohol, and this again into acetic acid, and finally decomposing the acetic acid itself, if its action be allowed to continue. it is important to the student to understand that this property of yeast is impaired or destroyed by strong alcohol, the stronger mineral acids, and a boiling temperature; all of which, therefore, should be avoided in its use.

Medical Effects and Uses

Yeast is moderately tonic and stimulant, probably in consequence of the alcohol and the bitter principle of hops usually contained in it. With a view to these properties, it has been employed in typhoid states of the system. it has also been used locally, in ill-conditioned and sloughing ulcers, to correct the fetor, and as a gentle stimulus to the debilitated surface. For this purpose it is employed in the form of a cataplasm, prepared by mixing it with meal. But it is introduced here simply for its property of promoting changes in starch and sugar, which may favour the complete digestion of these substances. Many years since, it occurred to me that we might possibly avail ourselves profitably of this property in the treatment of diabetes. It seemed, from the experiments of Dr. McGregor, to have been determined that, in diabetic patients, there was an abnormal tendency to the production of diabetic sugar in the stomach; and the inference seemed fair, that the disease might have its root in this disorder of function, and that the phenomena might result from the absorption of this saccharine matter into the blood, and its elimination by the urine. Dr. Gray suggested the use of rennet in order to promote the conversion of the gastric sugar into lactic acid. it occurred to me that a similar end might possibly be obtained by effecting its conversion, through the agency of yeast, first into alcohol and then into acetic acid; and another advantage from the yeast might be the speedy change of starch into sugar in the stomach, so that it should not pass unaltered into the bowels, and there be transformed into glucose, where there might not be forces in operation sufficient to effect its further normal transformation into acid. Under these impressions I made a trial of the yeast, and was much pleased with its apparent effects. The symptoms of the disease seemed to be rapidly ameliorated under its use, even when the patient was allowed a little farinaceous food. Others tried the remedy, with a similar amelioration of the symptoms. Unfortunately, however, the amendment has been but temporary; and I am unable to point to a single case, in my own experience, where a cure has been effected by the remedy. Nevertheless, I consider it as a useful adjuvant to other remedies in this disease, and would recommend a trial of it in all cases not advancing favourably under other treatment. The first notice of this use of the remedy, so far as I am aware, was in a communication made by myself to the College of Physicians of Philadelphia, and published in their Transactions (N. S., i. 390, Dec. 1, 1852). From a teaspoonful to a tablespoonful should be given three times a day, soon after each meal.