518 SUMMARY OF CURRENT RESEARCHES RELATING TO 



following method, communicated to him by Dr. H. Hager. The fluid or 

 its solution in absolute alcohol or benzol is treated with a few drops of 

 mercury nitrate. If the body Lave any affinity for oxygen a grey metallic 

 deposit is thrown down. 



The results which Dr. TJnna obtained with this test agree with the 

 long known experience that oil of cloves and oil of turpentine are inimical 

 to the anilin stains ; for while, on the one hand, cedar oil as a clarifying agent 

 and the hydrocarbons of the benzol-xylol series as solvents of the resins 

 are superior to the former ; yet on the other hand they show that the 

 affinity for oxygen is detrimental to the anilin stains, for glycerin and 

 carbolic acid, which, as is well known, quickly and permanently extract all 

 basic anilin dyes, do not possess according to Hager's test, any reducing 

 power. Together with the influence of oxygen there had been associated 

 as a matter of course the acid nature of the resins which were charged with 

 the decoloration of the preparations. Closer examination of the con- 

 ditions showed that the acid reaction in itself did not so much represent 

 the baneful factor, as rather the circumstance that the acids entered into 

 new and unstaiuable combinations with the basic anilin dyes which were 

 fixed in the tissues. In order to obviate as far as possible tlie latter con- 

 tingency, the resins must be freed from all traces of ethereal oils by 

 prolonged boiling and thickened to such a degree that they set imme- 

 diately when apjjlied to the preparation. But the deoxidation and the 

 action of acids are not the only influences which make themselves felt ; the 

 remains of the acids (HNO3HCI, acetic acid) used for the decoloration of 

 sections are probably more dangerous than all the resin acids. Therefore 

 for the removal of these residua the greatest care is required, for though we 

 may avoid, as far as possible, all the mentioned sources of decoloration, 

 there yet clings to the oil and balsam method the inconvenience of over- 

 removal of the stain owing to the use of alcohol unavoidably necessary for 

 dehydration. 



Dr. Unna has now contrived a method which renders unnecessary not 

 only the use of alcohol, but also the ethereal oils as clarifying media, 

 preparatory to mounting in balsam — the so-called dry method. Here the 

 stained sections, after decoloration by acid, and after staining with a second 

 dye, are taken dii'ectly from water to be placed on the slide, and having 

 next been carefully spread out and freed from superfluous water by 

 pressing them with tissue paper, are heated slowly and carefully over a 

 spirit-lamp to dryness. Upon the dried section and (if possible) warmed 

 slide is poured a drop of the balsam selected. With regard to the 

 permanence of the bacillar stain, the dry method, as far as can be 

 gathered from Dr. Uuna's comparative preparations, is not more effi- 

 cacious than the oil method when carried out with the precautions 

 insisted on by him. Yet the former, according to Dr. Unna's researches, 

 which he reports in another treatise immediately following the one under 

 discussion, and the contents of which cannot here be examined, should 

 have, apait from their simplicity, the economy of material, time, and 

 trouble, a noteworthy advantage for the recognition of micro-organisms 

 and their relations to the tissues. 



In a retrospect on the results thus obtained Dr. Unna gives detailed 

 directions for carrying out both the dry and the oil methods, as modified 

 according to the principles of the above-mentioned precautionary measures. 



Solution of Hypochlorite of Soda with excess of chlorine as a De- 

 colorizer.* — This solution is prepared by dissolving 8 parts (»f caustic 



* Journ. lie Microgrniiliic, xi. (1887) pp. 154-5. 



