70 NORMAL HISTOLOGY. 



formation of these cells into red blood-cells has 

 never been directly observed, and as the peculiar 

 appearance which they present can be accounted for 

 on other grounds, the formation of red blood-cells 

 in the marrow, while not improbable, cannot yet be 

 regarded as definitely demonstrated. 



TECHNIQUE:. 



Decalcified Bone. To obtain a general view of the struc- 

 ture of bone, we have recourse to transverse and longitu- 

 dinal sections of one of the long bones (from man or the 

 lower animals, such as the rabbit or dog), which has been 

 freed from its lime salts by soaking in dilute acids, and 

 rendered so soft as to be readily cut with a razor. 



Although various acids, such as nitric and hydro- 

 chloric, effect the decalcification of bone, solutions of 

 chromic or picric acids are preferable, because, while 

 very perfectly removing the lime salts, they harden and 

 preserve the soft structures in a most satisfactory manner. 

 As the salts of lime, as they exist in bone, do not undergo 

 rapid solution in these acids, the bits of bone which are 

 to be decalcified should be small, or the process will be a 

 very protracted one. They should not, at most, be larger 

 than a cubic centimetre. The quantity of fluid should 

 also be quite large (200 to 300 cubic centimetres to a bit 

 of bone of the above size). Picric acid, although slow 

 in its action, is, on the whole, to be preferred, because 

 the chromic acid often leaves the tissues in a granular or 

 cloudy condition, which interferes with subsequent study. 

 If chromic acid be employed, the bit of bone is put first 



