STAINING AGENTS AND METHODS 27 



tion and allowed to remain twenty -four hours. The bottle con- 

 taining the whole should be well corked, to prevent evaporation. 



The tissue after infiltration is to be placed on a wooden block, 

 and allowed to remain in the open air for a few minutes, after 

 which it should be plunged into a mixture of alcohol two parts7 

 water one part. Here it may remain for twenty -four hours, or 

 until wanted. 



Cut in the usual way, using a mixture of alcohol two parts, 

 water one part, for flooding the knife. The section should be 

 finally preserved in the same instead of pure alcohol, which would 

 dissolve the celloidin. 



In infiltrating the tissue with the collodion it is best, especially 

 if it be very dense in parts, to use first a thin and subsequently 

 the thick solution. A more perfect infiltration is often obtained 

 in this way. In some cases we have been obliged to continue the 

 maceration for several days. The solution should be kept in well 

 stoppered bottles, as the ether is exceedingly volatile. Should the 

 collodion at any time become solid from evaporation, it may be 

 easily dissolved by adding the ether and alcohol mixture. 



The process is of inestimable value where delicate parts are 

 weakly supported, and where it is important to preserve the normal 

 relations. The gelatin -like collodion permeates every space, and 

 as it is not to be removed in the future handling of the sections, 

 it affords a support to portions that would otherwise be lost or 

 distorted. It offers no obstruction to the light, being perfectly 

 translucent and nearly colorless. 



STAINING AGENTS AND METHODS 

 STAINING FLUIDS 



It is a very interesting fact (and one upon which our present 

 knowledge of histology largely depends) that, on examination of 

 tissues which have been dyed with special colored fluids, the dye 

 will be found to have colored certain anatomical elements very 

 deeply, others slightly, while others still remain unstained. 



Certain dyes are called general or ground stains, because 

 they stain all parts of a tissue alike, or nearly so. Others, which 

 are entitled selective, exhibit an affinity for some particular struc- 

 ture, usually the nucleus of the cell. Haematoxylin, or logwood, 

 for instance, has such an affinity for nuclei. The whole nucleus is 



