REACTION OF LYMPHATIC ENDOTHELIUM 437 



the form of fat or of erythrocytes and when this stimulus was 

 situated at some distance, these processes enlarged, acquired a 

 lumen and grew further. In the process of taking up of red 

 blood cells, the lymphatic is actively phagocytic; in the taking 

 up of the fat, the Ij^mphatic is assisted by leucocytes and appears 

 to absorb the substance in a soluble form. Otherwise, the two 

 reactions are identical and both are exactly similar to the nor- 

 mal growth processes for lymphatic capillaries, which have been 

 described fully in previous communications, the only apparent 

 difference being that in the present experiments, as well as in 

 the observations on the taking up of red blood cells, the stimulus 

 to growth is a visible one. These experiments seem to add 

 new weight to the hj^pothesis, proposed in 1909 (3), that the 

 growth of lymphatic capillaries, after their primary differentia- 

 tion, is inseparably connected with their function (i.e., with ab- 

 sorption) and that it is the varying formation of certain sub- 

 stances in the tissue spaces which regulates the growth of the 

 lymphatic capillary. 



As to the precise nature of the reaction; whether the lym- 

 phatic endothelium is attracted by the specific chemical sub- 

 stances, that is, whether they exert a positive 'chemiotactic' 

 influence on the lymphatic, or whether it is mainly a response 

 of the lymphatic to the quantity of substances moving toward 

 it and being absorbed, is impossible, on present evidence, to 

 decide. The fact that blood vessel endothelium failed to grow 

 toward the injected fatty substances, while lymphatic endothe- 

 lium did the reverse, is in favor of an especial relationship be- 

 tween these substances and lymphatic endothelium. In all 

 probability, it will be found that it is both a qualitative and 

 quantitative reaction; that certain groups of substances, among 

 them the fatty substances used in the present experiments, are 

 attracted to and absorbed bj^ lymphatics, and that extension of 

 the lymphatic takes place when the rate of absorption exceeds a 

 certain point. It is hoped that further experiments will help to 

 answer some of these questions. 



THE AMERIC.VN JOURMAL OF ANATOMY, VOL. 21, NO. 3 



