434 ELIOT R. CLARK AND ELEANOR LINTON CLARK 



growth on tlie part of the lymphatic endotheUum. However, in 

 experiments in w'hich the site of the injection was located at some 

 distance from the lymphatic, a definite growth of lymphatic 

 sprouts toward the fat was observed and this growth continued 

 after all of the injected droplets had been engulfed by leucocytes 

 (fig. 5). When one of these rapidly absorbable emulsions was 

 injected near the tip of a lymphatic, as in the series shown in 

 figures 8 and 9, the lymphatic sent out a fine process in the 

 direction of the nearest pigmented leucocytes. 



Blood vessels and mesenchyme cells were never observed to 

 react in any way to the presence of the cream or yolk of egg. 



In comparing the results obtained from the foregoing experi- 

 ments, it is evident that the reaction of the cells and tissues of 

 the tad-pole's tail was essentially the same in the case of all 

 the substances tried. Any difference in response w^as one of 

 degree and not one of kind. In general, the presence of the 

 injected fat called forth a response on the part of two types of 

 tissue — lymphatic endothelium and leucocytes. Connective tis- 

 sue cells did not react, in any observable manner, even w^hen the 

 injected globule or mass of droplets pressed against them. Al- 

 though it is not impossible that the blood capillaries may have 

 taken some part in the absorption of some of the soluble products 

 of the lipoiysis, the blood-vessel endothelium did not send out 

 sprouts or processes nor show^ any visible reaction to the pres- 

 ence of the fatty substance. Since the reaction of living cells 

 and tissues, to substances selected for the experiments was con- 

 fined to lymphatics and leucocytes, and since fat injected subcu- 

 taneously appeared to be absorbed through the combined efforts 

 of these tw^o types of cells it is desirable to give a more detailed 

 account of the reaction (1) of lymphatics and (2) of leucocytes, 

 tow^ard the injected fat. 



THE REACTION OF THE LYMPHATICS 



Lymphatic endothelium reacted positively tow^ard all of the 

 fatty materials used in these experiments. Wlien the sub- 

 stance had been injected near a lymphatic capillary, a fine 

 pointed process was sent out from the lymphatic, which ex- 



