GENERAL METHODS OF INVESTIGATION, BY S. STHICKER. XXvii 



examined with transmitted light, it is necessary, unless they 

 are extremely thin, to add some highly refracting fluid. In 

 the so-called parenchymatous organs as the liver, spleen, and 

 others in the parts of the central nervous system, and in bones 

 nothing is usually to be seen, either in the fresh or in the 

 hardened condition, so long as the connection of the morpho- 

 logical elements is not disturbed. It is requisite, in such in- 

 stances, either to tease out small portions with needles, or to 

 cut very thin sections. 



a. THE PREPARATION OF SPECIMENS BY TEASING. Speci- 

 mens may be prepared in this way on the slide, a very small 

 quantity of fluid being added : A minute fragment of the tissue 

 should be placed on the drop, and then seized and torn by two 

 sharp needles. Fibrous tissues can then be unravelled, as far 

 as the vision of the observer and the optical means at his dis- 

 posal will allow. The breaking up of tissues in this way is, 

 however, accomplished, as a general rule, with less ease when 

 fresh than after they have been macerated. The connecting 

 substances which unite the formed elements are frequently of 

 too firm a consistence to allow of their being thus torn, and 

 the latter, therefore, are the first to yield, so that it is rare to 

 see the formed elements whole and perfect. In such cases it 

 is expedient to macerate the tissues for some time, in order to 

 effect the solution of their connecting material. Solutions of 

 potash have been applied, with this object in view, as well as 

 of hydrochloric acid, bichromate of potash, Miiller's fluid, and 

 very recently, with excellent results, iodized serum. Lime or 

 baryta- water is to be recommended for the isolation of the 

 fibrils of connective tissue, whilst for the separation of the fibres 

 of transversely striated muscles the tissue should be macerated 

 in very dilute sulphuric acid, at a temperature of 40 C. ; or it 

 may be boiled in a mixture of chlorate of potash and hydro- 

 chloric acid. The most delicate manipulation of all is required 

 for the isolation of nerve cells and their processes. 



b. THE PREPARATION OF SPECIMENS BY SECTION. It is 

 only in some rare instances that sections can be made of animal 

 tissues, either when fresh or after maceration, of sufficient deli- 



