<)6 



George Heiier. 



it is easy to distinguish the vein and thus avoid it. In Fig. 2 is 

 shown, a section of an embryo 20 mm. long, taken at the level of 

 the apex of the lung, to show the thoracic duct in its relation to the 

 aorta and to the azygos veins. It shows why it is necessary to 

 insert the needle behind the aorta. It is best to use the finest 

 possible needles; my injections are made with No. 28. For an 

 injection mass either saturated aqueous Prussian blue or India 

 ink are used ; the Prussian blue gives beautiful total specimens which 



Fig. 2. — Transverse section of an embryo pig, 2 cm. long at the level of the 

 apex of the lung to show the relation of the thoracic duct to the azygos veins 

 and to the aorta, x 50. A., aorta ; a. v., azygos vein ; E., esophagus ; p. c, 

 pleural cavity ; t. d., thoracic duct ; v. c, vertebral cartilage. 



can be kept either in formalin or hardened in bichloride acetic and 

 kept in alcohol; the India ink runs farther, and the total specimens 

 can be cleared by the Schultze method. The ink is more useful 

 for determining complete injections. 



For studying the development of the lymphatics to the intestine 

 it was found best at first to inject by means of the thoracic duct 

 in embryos from 3.0 to 12.5 cm. Subsequently after the exact 

 position of the retroperitoneal sac was determined, it proved that 

 it was far better to introduce the needle directly into the sac. This 



