1891.] MICROSCOPICAL JOURNAL. 35 



Mite-Parasite of House Fly {Acartts Sp.P). — This specimen is 

 on a fnii^tncnt of the winj^ of the unfortunate fly with its proboscis in- 

 sertetl in a mid-vein where it can suck the life-blood of the fly. Beetles 

 may often be seen absolutely loaded by a species which preys on them. 

 I liave seen a fly with nineteen of them. Usually a single fly has but 

 one or two. They seem most numerous in the fall. Place the fly on 

 a shallow saucer with a little turpentine ; decapitate the fly and these 

 parasites will generally crawl ofl' and desert the sinking ship. — L. A. 

 Willson. 



[To be continucd.~\ 



Hints on Histological and Pathological Technique. 



By Dr. W. C. BORDEN, U. S. A. 



FORT DAVIS, THX. 



Hardening. — I. Use aqueous hardening fluids, if it is desired to re- 

 tain the tissue elements in their most unshrunken condition and tissue 

 relations undisturbed. 



All hardening fluids, which contain alcohol, when applied directly 

 to fresh tissues, cause them to shrink perceptibly, on account of the 

 rapid abstraction of the water ; but when used after the tissues have 

 been fixed by one of the aqueous fluids, such as Miiller's fluid or solu- 

 tions of osmic or picric acid, shrinkage is either entirely avoided or is 

 so slight as not to be detrimental. This is of particular importance in 

 embryological work, as well as in all tissues containing cavities, as 

 there is then less danger of distortion from the unequal shrinking ac- 

 tion of alcohol on the diflerent elements, and less likelihood that cavi- 

 ties will assume unnatural shapes. Delicate tissues and embryos, made 

 up as they are of widely diflerent elements, are bound to shrink une- 

 qually under the primary use of alcohol, so producing distortion, which 

 leads to erroneous results. 



Paraffine Imbedding. — I. In order that the section knife may glide 

 easily and smoothly through the tissue use turpentine to remove the al- 

 cohol. 



Chloroform and benzole are not as good as turpentine for putting the 

 tissue in the best attainable condition for cutting, as after their use the 

 knife does not pass through the tissue with the oily smoothness with 

 which it does after the use of turpentine. This is of importance where 

 large sections are to be cut, as the minimum amount of resistance to 

 the knife in proportion to the size of the section is in the highest de- 

 gree desirable. In order that the best results may be had. the turpen- 

 tine must be used in large quantity after fl(55(j/«/<7 alcohol, and must be 

 changed once in order to remove every trace of alcohol. With sonic 

 7ucthods of in toto staining (as will be indicated further on) turpen- 

 tine should fiot be uscd^ and then one of the other fluids must be re- 

 sorted to, but it is imperative for best results in all cases that the last 

 remnant of water be removed from the tissue by the sufficient use of 

 absolute alcohol before the turpentine or its substitute be applied, and 

 that sufficient of the latter agent chosen be used to entirely remove the 

 alcohol before paraftine comes into contact with the tissue. 



II. Do not pass a tissue directly from turpentine, chloroform, or 

 benzole into melted paraffine. 



