THE SINO-VENTRICULAR SYSTEM 153 



method than the fresher hearts. My experiences in this matter 

 are in accordance with Buhrm's work on the lymphatics for he 

 often noticed that the injection succeeds better ^'bei Leichen, 

 die schon etwas angefault sind, als bei ganz frischen." As a 

 matter of interest, hearts from other species were tested in a 

 manner similar to the injections made on beef hearts. Two 

 hearts from recently dead new born colts were tried but with 

 negative results although hearts from dogs, cats, sheep, calves 

 and swine were also tried with more or less satisfactory results. 

 Fresh human hearts were not obtained. 



The technique necessary for the injection of the sheath of 

 S.V.S. consists of apparatus and procedures similar to that ordi- 

 narily used in the study of the lymphatic system. The injec- 

 tions were made at all times with an ordinary No. 1 Luer hypo- 

 dermic syringe of 2 cubic centimeters capacity with the finest 

 steel needle obtainable. The most convenient manner of hold- 

 ing the syringe for careful injections was found to be similar to 

 that of holding a pipett, i.e., the barrel is held between the 

 thumb and middle finger with the index finger on the head of 

 the piston.- This position gives one the best advantage in hold- 

 ing the syringe in place after the needle is inserted and pressure 

 is brought to bear upon the piston. This detail is a matter of 

 no little consequence since the slightest movement of the syringe 

 after insertion of the needle may injure the sheath and cause 

 extravasation. As injection media, suspensions of India ink, 

 and Gerotas Prussian blue mass were used. For microscopic 

 study of the S.V.S. with the injection mass in place, India ink 

 proved to be the most satisfactory although Prussian blue was 

 used more extensively for study of the distribution of the system. 

 Gerota's Prussian blue injection mass was made up according 

 to his original formula : Two grams of Prussian blue with three 

 grams of turpentine were ground up in a porcelain mortar. The 

 mixture was then diluted with 15 grams of ether and filtered 

 through a fine cloth. This affords a mixture of low specific 

 gravity which penetrates into the very finest spaces. The solu- 

 tion will also keep for months if put in an air-tight jar. For study 

 of cell outlines within the sheath of the S.V.S., weak solutions 



