NERVOUS SYSTJ-M. 411 



49. Kidney tubules may be filled with indigo-carmine by 

 the method of Chrzonozczewski (45). 



50. Fresh semen may be obtained from the epididymis of a 

 rat, and studied in a drop of physiological salt solution. 



51. Ova may be studied in the fresh condition from the 

 ovary of a pig or cow. The liquor folliculi is allowed to escape, 

 and with it often comes the ovum surrounded by some cells of 

 the cumulus oophorus. 



52. Specimens of an injected placenta are instructive when 

 teased out to isolate the villi. 



11. SKELETAL SYSTEM. 



53. Red bone-marrow should be studied in the fresh condi- 

 tion in a drop of physiological salt solution. Fixed specimens 

 can also be made by the same methods as those employed in 

 the study of blood. In such slides stained in eosin and 

 methylene-blue, or with Ehrlich's triple stain, the various cellu- 

 lar elements can be made out. Bone-marrow may also be fixed 

 in Zenker's fluid and paraffin sections stained by one of the 

 above methods. 



54. For the study of the development of bone, the finger of 

 a human embryo three and one-half to five months old, or the 

 leg of a pig's embryo 10-15 cm. in length, is decalcified by 

 one of the methods described above after being fixed in 

 Zenker's fluid. Paraffin or celloidin sections are cut and 

 .stained in haematoxyliD and eosin, or in picro-carmine. For 

 the development of connective-tissue bones the parietal bone 

 of an embryo should be used. 



12. NERVOUS SYSTEM. 



55. To preserve the brain or spinal cord in toto, the most 

 useful agent is formol in 10 per cent, solution. Tissue fixed 

 in this may be used afterward for histological purposes, and 

 may be hardened in Miiller's fluid, etc. The tendency of 

 formol to cause tissues to swell may be counteracted by adding 

 an equal amount of 60 per cent, alcohol. 



56. For the fixation of nerve tissue for histological study, 



