234 THE CIRCULATORY SYSTEM. 



Fixing with Flemming's solution and staining with safranin is 

 the best method for studying the germ centers of the lymph-follicles. 

 Other fluids which bring out the mitoses may also be employed. 



Reticular tissue is best demonstrated by sectioning a fresh gland 

 with a freezing microtome, removing a section to a test-tube one-quarter 

 rilled with water, and agitating it. The lymphocytes are thus shaken out 

 of the meshes of the reticulum, leaving the latter free for examination. 



The same results can be obtained by placing a section prepared 

 in the above-named manner upon a slide, wetting it with water, and 

 carefully going over it with a camel' s-hair brush. The lymphocytes ad- 

 here to the brush. Both methods (His, 61) may be applied to hardened 

 sections which have lain in water for a day or so. In this case, how- 

 ever, the removal of the lymphocytes is not so easy as in fresh sections. 



In thick sections the reticulum is hidden by the lymphocytes. 

 If, on the other hand, very thin sections (not over 3 //) be made, especially 

 of objects fixed in Flemming's solution, the adenoid reticulum stands out 

 clearly without any further manipulation. 



The reticular structure may also be demonstrated by an artificial 

 digestion of the sections with trypsin. The sections are then agitated in 

 water, spread on a slide, dried, then moistened with a picric acid solu- 

 tion (i gm. in 15 c.c. of alcohol and 30 c.c. of water), again dried, cov- 

 ered with a few drops of fuchsin S solution (fuchsin S i gm., alcohol 

 33 c.'c., water 66 c.c.), and left to stand for half an hour. The fuchsin 

 solution is then carefully removed, the section washed again for a short 

 time in the same picric acid solution, then treated with absolute alcohol, 

 xylol, and finally mounted in Canada balsam. The reticular tissue of 

 both lymphatic glands and spleen are stained a beautiful red (F. P. 

 Mall). (See also page 129.) 



The treatment of splenic tissue is practically the same as that o* 

 the lymphatic glands. 



In all these organs (lymph-glands, spleen, and bone-marrow) a 

 certain amount of fluid may be obtained by scraping the surface of the 

 fresh tissue. This may then be examined in the same manner as blood 

 and lymph (see Technic of same). Sections of lymph-glands and spleen 

 previously fixed in alcohol, mercuric chlorid, or even in Flemming's 

 solution may be examined by the granula methods of Ehrlich. 



By using the chrome-silver method a peculiar network of retic- 

 ular fibers may be seen in the spleen. (Gitterfasern ; Oppel, 91.) 



The examination of the bone-marrow belongs also to this chap- 

 ter. The marrow of the diaphysis is taken out by splitting the bone 

 longitudinally with a chisel. With a little practice, it is easy to obtain 

 small pieces of the marrow, which are then fixed by the customary 

 methods and cut into sections. In the epiphysis the examination is 

 confined either to the pressing out of a small quantity of fluid with a vice, 

 or to the decalcification of small masses of spongy bone, containing red 

 bone-marrow. In the first case, methods applicable to blood examina- 

 tion are employed ; in the second, section methods (see also the petrifi- 

 cation method, page 132) are used. The methods given for the prepara- 

 tion of lymph -glands and spleen are also applicable in many cases. 



