3O2 PRACTICAL HISTOLOGY. [xxvu. 



colloid nature, and is then a pathological product. It is stained hy 

 logwood. Numerous sections of blood- and lymph-vessels outside 

 the basement membrane of the acini. 



12. Injected Thyroid (thickish section in balsam). (L) Numer- 

 ous large vessels in the connective tissue, with a plexus of capil- 

 laries over the acini, but outside their basement membrane. 



ADDITIONAL EXERCISES. 



13. Lung of Newt. (i.) This is an elongated sac, and is of comparatively 

 simple structure. Fill a lung with gold chloride (.5 per cent.), and suspend 

 it in a few cc. of the same Huid for twenty minutes. Reduce the gold by 

 exposure to sunlight in water feebly acidulated with acetic acid. Mount a 

 portion of the thin wall in glycerine. 



(a.) (L) Observe islands or small groups of epithelial cells. They lie in the 

 intercapillary spaces. The capillaries are wide, and form an anastomosing 

 network. Outside this capillary layer is a layer of smooth muscle, and one of 

 fibrous tissue. 



(ii.) If the gold chloride be reduced by formic acid (25 per cent, in the dark), 

 the epithelium lining the lung is shed, and then the nerves to the lung with 

 many ganglia in their course can be seen. 



14. Lung of Frog. (i.) Fill a lung with dilute alcohol, suspend it in the 

 same fluid (twenty-four hours), lay open the lung and pencil away the inner 

 lining epithelium and mount in Farrant's solution. 



(a.) (L.) Observe the large, coarse, but short primary septa, which project 

 inwards from the wall of the lung towards the large central cavity. From 

 them secondary septa pass to form a trabecular arrangement, thus giving the 

 interior of the lung a honeycomb-looking appearance. The trabeciilae consist 

 chiefly of smooth muscle. 



(ii.) The nerves of the frog's lung are readily demonstrated by the gold 

 chloride formic acid method and the methylene-blue method. The numerous 

 ganglionic cells in the course of the nerves have a straight and a spiral 

 process. 



15. Elastic Fibres in Trachea and Lung. (i.) Stain a longitudinal section 

 of the hardened human trachea according to the method described in Lesson 

 X. 10. The elastic fibres become black. 



(ii.) Use the safranin method (Lesson X. 9). This shows beautifully the 

 arrangement of the fibres, now of a purplish or black tint. 



16. Elastic Fibres in the Lung. (i.) I have devised the following two 

 methods, which give good results: Make sections of a dried and distended 

 lung, stain, a section in dilute magenta, and allow the section to dry com- 

 pletely on a slide ; add balsam and cover. The elastic fibres are red, and their 

 arrangement can be seen with the utmost distinctness. 



(ii. ) Or. stain a section in methyl-violet, and clarify it wit i the aniline-oil 

 and xylol mixture (p. 123). 



