All histologists who have worked with the silver and sublimate methods of Golgi have experienced the great inconvenience arising from the facts that the preparations are not durable, and that in mounting them a cover-glass cannot be employed in the ordinary way. Preparations by the silver method generally remain in good condition for a somewhat longer period than those by the sublimate method; Golgi has indeed stated he has some which have remained unaltered for nine years. The sublimate method is now most commonly employed in the form of the modification of Cox, in which only one fluid is required instead of two. In preparing sections of tissues that have been kept for the necessary time in this fluid, it is practically essential to blacken the originally steel-grey deposit by one or other of the several methods by which this may now be done. Such preparations, when new, are probably unsurpassed by those obtained by any other Golgi-method; but, unfortunately, when mounted in the orthodox manner without a cover-glass, and in spite of the most careful attention to various other technical details that have been recommended for the purpose of increasing their durability, they almost constantly show disintegration of the black deposit in from four to six months, and are certainly absolutely useless within a year. Ever since Golgi's methods came into use, histologists have been endeavouring to find some means of overcoming this great disadvantage of want of durability of the preparations. The only measure of success that has so far been achieved is that obtained by means of various processes of gold toning. All gold methods are, however, notoriously uncertain in their results. This, of course, simply means that in carrying them out it is necessary to fulfil certain very precise conditions, and that these conditions are as yet imperfectly understood. Certainly the gold toning processes that have been recommended for rendering Golgipreparations permanent are no exception to this rule. Our own observations and experiments have been made chiefly upon sections of tissues preserved in Cox's solution, because we are convinced that Cox's method is for various reasons the most trustworthy process of this class that has yet been devised, and therefore the one most likely to be of service in studying pathological changes. We have tried the methods of Obregia and Golgi for toning sublimate sections with gold. With that of the former we have not had any success. On the other hand, with that of the latter (as briefly described in Jack's translation of Pollack's Methods of Staining the Nervous System) we have obtained some very beautiful purple-black preparations, which have now remained unchanged under a cover-glass for considerably over a year. In the great majority of instances, however, the results have been unsatisfactory, the deposit rapidly undergoing disintegration.
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