Such being the chemical facts, we must admit that no reliance can be placed in corrosive sublimate soaps as germicide agents.  It must not be supposed that this incompatibility interferes with the use of these soaps for general therapeutic purposes.  It is only the specific germicide value which is destroyed.  Since the fats used in soap manufacture yield oleic acid, we will have a certain amount of mercuric oleates formed together with stearate and other salts, and for purposes of inunction these salts might be efficient.  Still the physician would prefer, doubtless, to use the specially prepared mercurial.

In producing, therefore, a disinfecting soap, being debarred from using the metallic germicides, we are fortunate in the possession of a number of efficient agents, organic in character, which may be used without interference in soaps.

Among these are thymol, naphthol, oil of eucalyptus, carbolates, and salicylates.  There is no chemical incompatibility of these with soap, and as they are somewhat less active, weight for weight, than corrosive sublimate, they are capable of use in larger quantities with less danger, and can thus be made equally efficacious.

It is in this direction, therefore, that we must look for the production of a safe and reliable antiseptic soap.

There is not much exact knowledge as to the usefulness of such additions to soap as borax and glycerin.  They are frequently added, and highly spoken of in advertisements.  Borax is a mild alkaline body, and as a detergent is probably equivalent to a slight excess of caustic soda.  Glycerin, although originally considered an emollient, probably on account of its source and physical properties, is in reality, to some skins at least, a slight irritant.  It is, in fact, an alcohol, not a fat.  It does not pre-exist in fats, but is formed when the fat is decomposed by alkali or steam.

In ordinary cases, soap owes its detergent effect to a decomposition which occurs when it is put in water.

A perfectly neutral soap, that is, one which contains the exact proportion of alkali and fat acid, will, when placed in cold water, decompose into two portions, one containing an excess of the acid, the other an excess of alkali.  The latter dissolves, and gives a slightly alkaline solution; the former precipitates, and gives the peculiar turbidity constituting “suds.”  These reactions must be kept in mind in determining the effect of the addition of any special substance to the soap.—­The Polyclinic.

* * * * *

OPTICAL ERRORS AND HUMAN MISTAKES.[1]

  [Footnote 1:  Read before the American Association, Buffalo,
  August, 1886.]

By ERNST GUNDLACH.

I wish to call attention to a few mistakes that are quite commonly made by microscopists and writers in stating the result of their optical tests of microscope objectives.