294 CIRCULATION OF THE BLOOD. 



know, however, that it is to be found almost everywhere, par- 

 ticularly in the tunica adventitia of bloodvessels, underneath 

 the endothelial lining of serous cavities, and of the vascular 

 system, and on the surface and in the inter-fascicular splits of 

 tendons and aponeuroses ; and that, wherever it occurs, it is in 

 anatomical relation with lymphatic capillaries. The proof 

 that the absorption of solid matters in fine division takes place 

 mechanically, has already been given in Chapter VIII., where 

 it is shown that the lymphatics leading from the peritonaeum 

 can be filled with Prussian blue or other coloring matters in 

 suspension, by injecting the liquid charged with them into 

 the peritonaea! cavity; and that if the mechanical conditions 

 are favorable, the injection takes place in the same manner in 

 the dead body as in the living. It has also been shown in the 

 same Chapter, that in order to obtain good anatomical pre- 

 parations of lymphatic capillaries, the best method is that 

 there described as the method of puncture, the reason being 

 that, wherever these vessels are abundant, they are in open 

 communication with the canaliculi, and, consequently, that it 

 is impossible to introduce the point of a syringe into the tissue 

 bt'tweiMi them without penetrating many of these cavities. 

 This may be instructively shown as follows. 



84. Method of Showing the Mode of Entry of Col- 

 ored Liquids into the Lymphatic Vessels. The best 

 tissue for the purpose is the mucous membrane of the larynx 

 and trachea ; those of an ox or sheep may be used. An ordi- 

 nal 1 }' subcutaneous syringe, with as fine a point as possible, is 

 charged with solution of alkanet in spirits of turpentine. The 

 point is then inserted horizontally into the mucous membrane, 

 at some part where it rests upon cartilage. A drop of the 

 liquid is then pushed out into the tissue as slowly as possible. 

 If the operation is successful, it at once fills the lymphatic net- 

 work, the character of the result varying according as the 

 point of the syringe has entered the submucosa or has not 

 penetrated beyond the mucosa. That the liquid progresses 

 along the vessels by capillarity is learnt by observing that the 

 injection continues to spread long after all pressure from the 

 syringe has ceased. The alkanet solution is employed in this 

 and similar experiments, because it is quite incapable of pass- 

 ing through organic membranes, is immiscible with water, and 

 enters capillary channels with extraordinary facility. 



The further progress of liquids along the lymphatics towards 

 the venous system is due partly to capillarity, partly to the 

 fact that the lymphatics pass through spaces in which the 

 pressure is less than that in which their capillaries originate, 

 and parti}' to the variations of pressure due to muscular action, 

 to which they are subjected. That in certain parts of the body 



