WITH THE MICROSCOPE. IOI 



the aid of the muscles of the hand and arm, and the pressure can be 

 modified instantly, according to the judgment of the operator. 



188. Of Injecting the Ducts of Glands. The modes of injecting 

 which have just been considered, although applicable to the injection 

 of vessels, are not adapted for injecting the ducts and glandular 

 structure of glands ; for as the ducts usually contain a quantity of 

 the secretion, and are always lined with epithelium, it happens that 

 when we attempt to force fluid into the duct, the epithelium and 

 secretion are driven towards the secreting structure of the gland, which 

 is thus effectually plugged up with a material which is colourless. 

 There is therefore no hope of making out the origin of the ducts and 

 their relation to the secreting structure. It is obviously useless to 

 introduce an injecting fluid, for the greatest force which could be 

 employed would be insufficient to drive the contents of the follicles 

 and ducts through the basement membrane, and the only possible 

 result of such an attempt would be rupture of the thin walls of the 

 secreting structure and extravasation of the contents. As I have 

 before mentioned, partial success has been obtained by employing 

 mercury, but the preparations thus made are not adapted for micro- 

 scopical observation. 



I had long felt very anxious to inject the ducts of the liver in 

 order to ascertain the manner in which they commenced in the lobule, 

 and the precise relation which they bore to the liver cells. This has 

 long been a point of dispute among microscopical observers, ant 1 

 many different and incompatible conclusions have been arrived at b) 

 different authorities. In order to prove the point satisfactorily it was 

 obviously necessary to inject the ducts to their minute ramifications, 

 which no one, as far as I was able to ascertain, had succeeded in 

 doing satisfactorily. After death the minute ducts of the liver always 

 contain a little bile. No force which can be employed is sufficient 

 to force this bile through the basement membrane, for it will not 

 permeate it in this direction. When any attempt is made to inject 

 the ducts, the epithelium and mucus, in their interior, form with the 

 bile an insurmountable barrier to the onward course of the injection. 

 Hence it was obviously necessary to remove the bile from the ducts 

 before one could hope to make a successful injection. It occurred 

 to me, that any accumulation of fluid in the smallest branches of the 

 portal vein or in the capillaries, must necessarily compress the ducts 

 and the secreting structure of the liver which fill up the intervals 

 between them. The result of such a pressure would be to drive the 

 bile towards the large ducts and to promote its escape. Tepid water 

 was, therefore, injected into the portal vein. The liver became 

 greatly distended, and bile, with much ductal epithelium, flowed by 



