110 PRACTICAL HISTOLOGY. 



until the methods upon which they depend have been 

 described and explained. 



Preparation 11. Medullary tissue. Ordinary 

 marrow, which consists for the most part of adipose 

 tissue, is obtained from the long bones of most 

 animals. But the spongy tissue of the bones gene- 

 rally and the medullary canal of the long bones 

 in some animals the rabbit and guinea-pig, for 

 example are filled with red marrow, which con- 

 tains little adipose tissue, but is mainly made up 

 of the so-called proper marrow-cells, which are in 

 many respects similar to the pale corpuscles of the 

 blood, and, like these, exhibit amoeboid movements. 

 To see the marrow-cells, therefore, in their natural 

 condition the tissue should be taken quite fresh and 

 examined on the warm stage. The bone the femur 

 of a guinea-pig, for instance, preferably a young 

 animal having been removed and cleared of the 

 surrounding soft parts, is broken across, and a small 

 piece of the marrow picked out and broken up with 

 needles in a drop of serum or salt solution on a piece 

 of thin glass. A small piece of hair is then added, 

 and the preparation is covered ; a brush dipped in 

 oil is drawn round the edge of the cover-glass to 

 prevent evaporation, and the specimen is then placed 

 on the w r arrn stage (p. 30) and examined. The dif- 

 ferent sizes and varying forms of the marrow-cells 

 are to be noted, as also the large clear nucleus which 

 many of them possess, and which at once distin- 

 guishes these cells from the ordinary white blood- 

 corpuscles. But many are also observable which 

 are in every respect similar to the latter, and may 

 indeed not improbably belong to the blood, for the 

 bloodvessels are very large and numerous in the 

 medullary tissue, and yield the numerous red blood- 

 corpuscles which are seen scattered over the field. 

 Transitions may be observed between the proper 

 marrow-cells and the white corpuscles, and as they 

 both exhibit amoeboid movements it may be inferred 



