If expeditiously and properly done, the suppositories, when cool, should slip from the mould without the least trouble, having a beautiful polished finish, and, what is more important still, having a uniform composition and structure, and not with the active medicinal agent all concentrated at the apex, as is always the case when the heat applied has been excessive. The principal secret of making suppositories is to avoid heating the basis much beyond its melting-point and to keep it over the heat as short a time as possible. A thermometer to indicate the temperature of the water in the bath prevents a lot of worry. If a batch of basis- say, cocoa-butter- be accidentally overheated, it is well to put it aside and begin with a new piece. The overheated material regains its normal character as to solidification in about two days, when it can satisfactorily be used.

The Melting-point of cocoa-butter (about 930 F.) is lower than the normal temperature of the human body (980 F.), and the fat is in consequence considered to be an ideal basis for suppositories, but it is customary during the summer months and in warm countries to add from 1 to 3 grains of white wax to each 15-grain suppository in order to keep the mass firm; the addition does not imperil the therapeutic efficacy of the suppositories. Dispensers should, however, keep the fact in mind that some medicaments raise the melting-point of cocoa-butter, either by chemical action upon it or by retarding fusion. This matter was investigated by Mr. T. Maltby Clague (The Chemist and Druggist, 1891, 1. 800), and his results are well worth quoting. In 1890 a correspondent submitted suppositories prepared according to the following prescription, with the complaint that they remained solid in the rectum:

Misce et divide in suppositoria sex.

We found the melting-point of the suppositories to be 1130 F., so that it had increased by at least 180 F. Mr. Clague, taking the matter up, compounded several suppository-masses, kept them under observation, and noted that with the ingredients mentioned below the melting-points were raised as stated:

There seems no doubt that the rise in melting-point is due in these cases to interaction between the substances and the fat, metallic salts of the fatty acid being formed in some cases. Mr. Clague proved this with the bismuth, lead, and zinc suppositories, while the ferric salts doubtless raised the melting-point through the influence of their acid radicles. Probably owing to the publication of Mr. Clague's observations, such combinations are now rarely seen in practice. One may tell quickly whether a suppository will melt or not by placing a small piece of it in the mouth; should it remain hard, a little oil or lard must be added to the mass.