34 THE AMERICAN MONTHLY [Jan. 



The cement which I wish to bring before you is called Clarke's 

 Cement, and has been used by Mr. Thos. Clarke, of Birmingham, 

 lor the last sixteen years for mounting objects in methylated 

 spirit, and his slides are quite good and sound now. I have here 

 a slide of Leptodorahyalina mounted in alcohol by this gentleman 

 in 1887, or eight years ago, and it is perfect at present. This is 

 sufficient proof that the cement is reliable for spirit mounts^ 

 and, of course, also for all watery fluids. It is black, and used 

 like asphalt. The diluting fluid is turpentine or })enzole, both 

 of which dissolve it very readily. It sets quickly, but takes 

 two or three weeks to get sufficiently dry for handling the slides. 

 It is very tenacious and never becomes quite hard and brittle. 

 I usually fix the cover glass of fluid-cells with thickened Miller's 

 cement, and when dry make a ring of Clarke's cement over that. 

 Of course with alcohol mounts Miller's cement cannot be used, 

 and the cell can be made, and must be closed with Clarke's 

 cement alone. It is best to use the smallest oil-color sable brush, 

 putting on the cement very gradually and little at a time. The 

 brush can be waslied out from time to time in some benzole kept 

 for the purpose in a separate little bottle. 



The composition of the cement is quite unknown to me and 

 is a trade secret. The cement itself can be obtained from Mr. 

 Thos. Bolton, 25 Balsall Heath Road, Birmingham.— Chas. F. 

 RoussELET, F. R. M. S., in "Journal of the Queckett Micros. 

 Club." 



Technique for the Examination of Skin Bacteria. — The 

 important work done by Unna in the development of measures 

 for the study of the bacteria of the skin in pathological condi- 

 tions, has thrown great light upon the etiology of various der- 

 mal affections, the causes of which were formerly very obscure. 

 Previous to the improvements made by Unna, iodine and vari- 

 ous decolorizing solutions were employed. The method recom- 

 mended by Unna is termed by him the "para rose-aniline-iodine 

 method." The difficulty formerly experienced was in remov- 

 ing the iodine coloring matter without decolorizing the microbe. 

 An advantage was found in using a mixture of aniline oil with 

 acid pigments, instead of aniline oil alone. Unna prefers orange 

 eocene and picric acid. By the aid of this method it is possi- 

 ble to obtain and decolorize masses of dermal structures and 



