240 PRACTICAL HISTOLOGY. 



ous humor may be added to it. It is not possible to 

 preserve this preparation permanently. 

 Preparation 10. Artificial impregnation. 



If a preparation similar to that just described is ex- 

 amined on the warm stage at the temperature of the 

 body, and a little of the seminal secretion of a male 

 rabbit with the spermatozoa in full activity is added, 

 the penetration of these into the zona pellucida ot" 

 the ovum can be observed. 



Preparation 11. Section of uninjected testis. 

 The testis is one of the most difficult organs to 

 prepare, owing to the looseness of its structure. It 

 is firmest in those animals (cat, pig) in which the 

 peculiar, granular, polyhedral cells, which accom- 

 pany and surround the bloodvessels, are most nume- 

 rous. To harden it two or three cuts are made 

 almost through its whole thickness, and it is then 

 placed for ten days in 2 per cent, bichromate of pot- 

 ash solution, and afterwards in spirit. Sections of 

 both the body of the testis and the epididymis are 

 to be made. 



Preparation 12. Lymphatics of testis. In 

 the sections made as above there will be observed in 

 the interstices between the seminiferous tubules 

 large, cleft-like spaces, looking almost like acciden- 

 tal clefts in the loose connective tissue uniting the 

 tubules. They are in reality, however, the lacunar 

 commencements of the lymphatics. To show this 

 the following simple experiment may be performed : 

 In a recently-killed dog the fine canula of a Pravaz 

 syringe, filled with Berlin blue solution, is stuck 

 through the scrotum into the middle of the sub- 

 stance of one of the testes, and the solution is slowly, 

 and without exerting any considerable pressure, in- 

 jected into the organ. If the abdomen is opened the 

 blue fluid will soon be seen passing along the lym- 

 phatics which run in the spermatic cord, and from 

 these into those of the back of the pelvis and abdo- 

 men, at length reaching the thoracic duct. If now 

 the testis is removed and hardened in spirit, and 



