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mb^ aboulb not 3njccte& flDaterial 



be 1bar&eneb as carefully as ©rMnar^ /IDatenal ? 



By Prof. V. A. Latham, D.D.S., Chicago University. 



IT is time to consider the vast importance attached at the 

 present time to micro work, that greater attention should be 

 paid to the matter of hardening. Why this is so badly 

 attended to is scarcely to be understood. If it can be neglected 

 without detriment, why need we trouble to do it at all ? To this 

 many will answer, why, to keep the parts in a good condition. 

 Then is this true where the hardening is not thoroughly done ? 

 We aim to preserve the cells and tissues in as natural a state as 

 possible, to keep the tissue as near as possible to the original con- 

 dition, to prevent shrinkage of the elements ; and here we 

 require every care, so as to be able, in pathological growths, to 

 distinguish the particular kinds of neoplasm, as, for example, a 

 large or small round-celled sarcoma, or a spindle-celled from a 

 round-celled. These are important, and if badly hardened the 

 spindle-cells shrink so as to make them nearly round in appear- 

 ance. Injected material is useless for good histological or 

 pathological work, if not hardened well. 



A slide should show the cell and tissue-structure quite as 

 clearly as the course of the blood-vessels, lymphatics, or bile- 

 ducts, for otherwise we do not get the correct idea of their re- 

 lationship to the cells, etc. To-day the idea of a slide to show 

 injections, and another for the structure, is out of place, when 

 they both can be so well done. Alcohol is only permissible as a 

 hardening agent in very small, thin pieces of tissue, where rapid 

 examination for diagnosis is desired, and here very great care 

 should be used to have the alcohol in varied strengths, using a 

 weak solution for a few hours, a stronger for a little longer time, 

 until complete hardening is done in strong alcohol. The abstrac- 

 tion of the water from the tissues by the alcohol, and its power of 

 coagulation, rendered it a little dangerous for hardening for 

 diagnosis, or for preserving micro-organisms in the tissues. 

 Chromic acid, i/6th per cent. (2 parts of solution of acid and i of 

 spirit, stir), as advised by Klein, is decidedly one of the best and 

 most reliable agents known, but it has its objections — that the 



