436 ELIOT R. CLARK AND ELEANOR LINTON CLARK 



lymphatic and one of its main branches extended nearly to the 

 injected globule. A record made eighteen hours later showed 

 that, from the tip of the lymphatic, a new branch had been sent 

 out to the left, on the side toward the oil globule, which had 

 already extended some distance in the direction of the oil globule. 

 Three days after the injection, this newly formed lymphatic 

 sprout had reached the pigmented leucocytes surrounding the 

 oil globule. While this sprout, during its growth toward the 

 oil globule sent out a branch in the opposite direction, its unin- 

 terrupted extension to the oil indicates, pretty definitely, that the 

 presence of the oil exerted on it an attractive influence. The 

 blood vessel sprout, in the meantime, retracted steadily. This 

 retraction may have had nothing to do with the presence of the 

 oil, as such new blood vessel sprouts have often been observed 

 to retract. Considered, however, in connection with the record 

 shown in figure 2, it is suggested that possibly the oil exerts a 

 repellant influence on blood-vessel endothelium. 



The attraction of injected fatty substances for the lymphatic 

 endothelium continues after the fat droplets have all been taken 

 up by leucocytes, since in the case of the cream and yolk, injec- 

 tions, made at some distance from a lymphatic, a sprout continues 

 to grow toward the site of injection when extra-cellular fat is no 

 longer present. In such cases, many of the pigmented leu- 

 cocytes scatter, part of them moving toward the lymphatic. 

 Some become clear during the migration and it is probable that 

 the soluble, and therefore invisible, substances, set free from the 

 leucocytes, exert this attraction on the lymph sprout. It should 

 be mentioned in this connection, that even in its response tov/ard 

 the more slowly absorbed substances, the lymphatic capillary 

 comes into contact with the pigmented leucocytes surrounding 

 the olive oil, or sodium oleate, rather than with the fatty sub- 

 stances themselves. 



The manner in which the lymphatic reacts toward these 

 various substances is very similar to its response toward the ex- 

 truded red blood cells, described in 1909 (3), and referred to 

 earlier in the present article. In both cases, the lymphatic 

 sent out fine processes toward the external stimulus present in 



