160 Transactions of the Society. 



these reasons it is preferable to transfer the sections, either single 

 or stuck to slides by the albumin method, through xylol and 

 alcohols of decreasing strength into distilled water, and tone them 

 by means of a 0*1-0 -2 p.c. acid solution of gold chloride, as 

 suggested in my communication to the January Meeting of the 

 Physiological Society, at which a preliminary note on the above 

 described method was also communicated. The unstable reduced 

 silver may be fixed by other methods, e.g. by the toning and 

 bleaching process of Veratti, as published by Golgi, which has the 

 advantage of imparting to the finished preparations a white, almost 

 colourless background, though I find it rather more difficult of 

 execution, and more expensive on account of the greater quantity 

 of gold chloride solution required. The toned preparations can be 

 either dehydrated and mounted or counterstained, as one may think 

 desirable, the consecutive treatment being according to the stain 

 chosen. For routine work I prefer alum-carmine, because it allows 

 the handling of many sections or slides at the same time, does not 

 usually require a successive differentiation, and imparts to both 

 nuclei and cytoplasm a deep pink staining contrasting well with 

 the black or dark grey colour of the apparatus. For the dehydra- 

 tion of sections stained with alum-carmine no absolute alcohol is 

 required, as after the 95 p.c. alcohol clearing in carbol-xylol and 

 mounting in balsam may follow. 



5. General Considerations. 



The present method is only a modification of the uranium 

 nitrate method proposed by Cajal, who had already suggested the 

 use of other nitrates, such as those of manganese and of lead. 

 Various attempts were made by me with copper nitrate, but 

 unsuccessfully. The same can be said of cobalt sulphate. Cobalt 

 acetate I am still investigating, as it appears to be particularly 

 suitable for the study of the internal apparatus in generative 

 organs, and enables one to recognize in the middle piece of 

 spermatozoa a very small structure, similar to a minute apparatus, 

 to which I paid special attention after having seen some preparations 

 of Dr. J. Bronte-Gatenby. 



Cobalt nitrate, like uranium nitrate and arsenious acid, does 

 not alter the Nissl's substance, as can be shown by counter-staining 

 toned sections of spinal ganglia or spinal cord with neutral red, 

 toluidin blue, crystal violet, etc. Much the same might be said of 

 neurofibrils, on which subject, however, I propose to give a special 

 demonstration in due course. 



As pointed out in my preliminary communication, my method 

 stains in certain conditions not only the internal apparatus, but 

 also intracellular formations, which, according to their morphology 



