This section is from the book "A Practitioner's Handbook Of Materia Medica And Therapeutics", by Thos. S. Blair. Also available from Amazon: A Practitioner's handbook of Materia Medica and Therapeutics.
Extracts, as made by the usual U. S. P. methods honestly followed, seldom disappoint. Unfortunately, poor materials, sophistication, and quick but defective processes characterize the manufacture of the great bulk of solid and fluid extracts upon the market. As an illustration of approved processes for the making of extracts upon a large scale, we reproduce from "Red Cross Notes," Series V, NO. 3, the following: "By the term extraction is meant the operation which has for its object the separation of the physiologic and therapeutic principles of the drug by treating it with liquids capable of holding these tinctures in solution.
"The extraction and the separation of the chemic constituents of drugs is a comparatively simple problem, but, as is well known, the chemically evolved products differ quite materially, in many instances, from the structure itself. So the pharmaceutic preparations of the drug may differ in purpose and action from the products that the chemist breaks out of the plant. Professor Lloyd has well stated that 'the sum of the fragments (chemic constituents) that may be broken out of a plant structure by chemic methods, although possessed of marked characteristics (and some of them energetic physiologically) is not representative of the full therapeutic energy either of the plant or the ordinary pharmaceutic preparations.' "The general process of extraction may be described as a modified repercolation or fractional percolation, and is in brief as follows: "The drug is bulked, mixed, dried and ground, and then assayed. The ground drug, in lots of two hundred and fifty pounds, is moistened with the menstruum. This moistening is accomplished in a rotary mixer run by power. . . . The moistened drug is packed in conical iron percolators, porcelain-lined, with vapor-tight covers.
"After sufficient maceration the percolation proceeds. The menstruum is fed to the percolators by a system of pipes. At the end of the row of percolators are two large measuring tanks being fed from larger tanks containing the main supply of the menstruum. . . . The menstruum, or the first percolate is a weak percolate from a previous percolation. This first percolate is a concentrated fluid extract. When two hundred and fifty pounds of concentrated percolate have been collected, it is reserved for concentration to a solid extract."
As will be seen, this process describes the extraction of a fluidextract without the aid of heat. To convert this into a solid extract, the drug in the percolators is exhausted, the weak percolate going into the next percolator, while the concentrated fluidextract is concentrated at the lowest possible temperature, the alcohol being recovered. This is done with elaborate vacuum concentrators, and each batch of solid extract is assayed.
To make a solid extract some heat is necessary, but, with the exception of a very few drugs, there is no excuse for employing heat in the making of fluidextracts. Numerous criticisms have been made of fluidextracts. We will consider in detail the more reasonable ones, but it must be borne in mind that in approving fluidextracts we have in view none but high-class products. A leading criticism is that all official fluidextracts are made from the dried drug, and therefore, in a number of instances, are not sufficiently active. Until recently this was the case, but several enterprising manufacturers now offer a list of green plant fluidextracts, the principal ones being black haw, cimicifuga, cactus, corn silk, cotton-root bark, echinacea, gelsemium, passion flower, poke root, stillingia, and saw palmetto.
The fact that large manufacturers enjoy superior facilities in purchasing and promptly working up the crude drug militates in favor of the modern machine-made fluidextract over those made in small quantities in retail pharmacies. A second criticism is that fluidextracts contain a large proportion of useless extractive, inert resins, starch, gum, pectin, coloring matter, and plant detritus generally. This argument certainly does strongly apply against the cheaper grade of fluidextracts, but those made of strong grain alcohol and without the aid of heat contain no greater relative proportions of these inert matters than do tinctures. Naturally, both of them carry a fair proportion of these inert substances, even with careful preparation; but various makers have directed much intelligent effort towards the perfecting of certain fluidextracts and tinctures; and preparations such as Parke, Davis & Co.'s cascara, Squibb's ergot, and Norwood's veratrum, are to the credit of American pharmacy.
Another objection is that the fluidextracts of plants not very extensively used in regular practice are not of the high quality of those more commonly employed. This valid objection is hard to meet with a practical solution. Many unavoidable reasons conspire to make it frequently the case that these products are either inferior when first made or become so by being long kept in stock. Probably it is wise to procure such fluids from the manufacturers direct or to employ fluids emanating from sectarian sources when drugs are wished largely employed by sectarians and but little used by regular physicians. A last objection is that fluidextracts so frequently precipitate or become muddy. Cheap and poorly made ones do so to an annoying degree. The best ones do so at times. It must be remembered that they are very concentrated preparations, and usually the sediment will again enter into solution when incorporated with a solvent. Certain plants contain matters liable to gelatinization, and they spontaneously decompose, when incorporated with a fluid medium, into a worthless brown magma with which nothing can be done. Iris, geranium, stillingia, cotton-root bark, and urticaria are peculiarly liable to this to change. Extractive matter and tannates precipitating gradually in some high-grade fluidextracts can be re moved by filtration oft times to the advantage of the product. Such substances as cannabis indica or ipecac should not be filtered to remove precipitates from their fluid preparations.
As a practical matter of fact, the little sediment existing in high-class products is not of great consequence when one is prescribing for the action of remedies in the usual or the large dose.