370 SOME HARDENING AGENTS. 



placed in separate bottles, duly labelled. The same remarks apply 

 to tissues removed by operation. They should be placed in the 

 hardening fluid at once ivithout more handling than is absolutely 

 necessary. 



If the tissues are placed in a strong solution — such as a one 

 per cent, solution of chromic acid or in alcohol — the elements of 

 which they are composed shrink on the outside and undergo such 

 alterations as render it impossible to form a correct idea of the 

 pathological change that has taken place. Bad hardening and 

 staining, combined with imperfect histological knowledge, will 

 account for most of the extraordinary fallacies that have been 

 made public of late years. 



Although in this country (U.S.A.) autopsies are obtained with 

 difficulty, still many are made, and the results are rendered useless 

 by the bad hardening of the material and other causes. The 

 amount of pathological material annually wasted in this way is 

 enormous, and the hindrance to the advancement of our knowledge 

 of disease is very great. 



The object of hardening is not only to give the specimens 

 greater consistency, so that thin sections may be more easily 

 obtained and more safely manipulated, but also to fix the tissue- 

 elements as far as possible, in the same relative position as in the 

 living body. The hardening process also acts on the protoplasm 

 of the cells and prevents their swelling up when placed in water 

 and various staining fluids. The hardening fluid used must be one 

 which will not itself injure the specimen, and which can be tho- 

 roughly removed by washing in water, in order that it may not 

 interfere with the staining operation. 



Hardening may be accomplished either by freezing or by 

 various chemical re-agents. The latter act by coagulating the 

 albumen, by withdrawing the water, or, in some instances perhaps? 

 by combining with the albumen to form a harder compound in a 

 manner comparable to the process of tanning, and therefore the 

 choice of a suitable re-agent in each case will be found, in spite of 

 anything said to the contrary, to be a matter of considerable 

 moment, and its mode of use equally important. 



Enormous labour has been incurred by one generation of 

 investigators in correcting the errors of a previous generation, who 



