2650 Journal of Applied Microscopy 



changes in the central nervous system is practically eliminated. The processes 

 of digestion and absorption are arrested and fixed in the act, and tissues may 

 thus be secured in any desired stage of physiological activity. Engorged tissues 

 are caught with the blood in them, giving a picture of rare beauty. Blood and 

 bone marrow are perfectly fixed. 



For studying bone marrow the ribs of a kitten or baby rabbit fixed with 

 HgCl2 will decalcify over night in a solution of 3 per cent. HNO,^ made up with 

 67 per cent, alcohol, and from such ribs, sections 3^/^< may be secured easily, 

 giving a picture of bone marrow with its connective tissue framework normally 

 distended and marrow elements in normal position. On sections so thin an oil 

 immersion objective may be used, blood stains employed, and eosinophilic cells 

 in great numbers may be demonstrated outside the blood vessels of the bone 

 marrow. Particularly are these marrow elements, together with nucleated red 

 blood corpuscles, shown with great beauty in the ribs of a 10 cm. embryo pig. 

 Bone marrow in this form is a decidedly different tissue from bone marrow 

 studied as a smear. 



The thoracic wall of a small white rat, tixed by injection of Hermann's fluid, 

 may be cut at 3i/< without decalcification, and, stained with iron hematoxylin, 

 shows not only marrow elements, but the intercostal muscles and nerves in nor- 

 mal position with the usual beauty of a Hermann's fluid fixation. In short, we 

 get a penetration with Hermann's fluid impossible by the ordinary method of 

 using it. 



There is scarcely a tissue that is not shown with new beauty by this method 

 of fixation. Sections of lung fixed by HgCU injection and cut at 3i/< give a 

 picture unequalled in beauty. The epithelial lining is intact and shows the 

 more perfectly in that the tissue is at normal distention. 



A brain fixed and hardened in situ presents a very different appearance 

 from a brain supported on a sheet of cotton. 



The method is invaluable not only in preparing tissues for classes in histol- 

 ogy, but also as a research method. 



In the use of HgClo as a fixer by the usual method, the crystalline deposits 

 formed are very annoying and detract from the value of the fixer. This difficulty 

 is overcome in the simplest manner. At a pressure of 130 mm. mercury, 400 c. c. 

 of a saturated aqueous solution of HgCl2 are injected in about 10 minutes into a 

 small kitten or rabbit, the time depending somewhat on the freeness of the 

 venous opening. If the venous opening is not sufficiently free an oedema is likely 

 to be caused, which in some cases is no disadvantage. Follow the injection of 

 the HgClg by an injection of 500 c. c. of 67 per cent, alcohol. This not merely 

 washes out the HgClj, but the HgC^ is about 3 times as soluble in alcohol of 

 this strength as in water, so the washing out is doubly effective and the harden- 

 ing of the tissue is begun at the same time. After such a washing out, if prop- 

 erly done, one may cut out whatever tissues desired without blackening the knife 

 or tissues. It is usually best to leave the tissues in 67 per cent, alcohol for one 

 day, though, if necessary, they may be transferred at once to 82 per cent, alco- 

 hol after having been washed out with 67 per cent, alcohol. 



It is found best to inject only one-half an animal at once. The canula 



