622 SPECIAL PHYSIOLOGY. 



however, the absorptive power of the lacteals is much more limited 

 than that of the veins. First, with regard to poisons : in experi- 

 ments, the opposite of that just recorded, the arteries and veins of a 

 piece of intestine, isolated by two ligatures, have been tied, whilst the 

 rest of the mesentery, containing the lacteal vessels, has been left 

 untouched; poison then introduced into the intestine is not absorbed, 

 so as to destroy the animal, until, by loosening the threads on the 

 bloodvessels, blood is again allowed to flow through them. (Magendie 

 and Segalas.) To such experiments it has been objected, that tying 

 the bloodvessels suspends the functions of the lacteals, which may 

 lose their absorbing power when the capillary circulation around them 

 is stopped. The experiment has, therefore, been varied, so as to per- 

 mit the local circulation to continue ; thus, the vein from the part of 

 the intestine into which the poison is introduced, is first compressed, 

 and then opened below the point of compression, so that the blood re- 

 turning along it escapes, and does not enter the general circulation, 

 although the local circulation in the intestine still goes on. Under 

 these conditions, no poisoning takes place, but this speedily happens 

 when the pressure on the vein is removed, and the blood returning by 

 it, enters the general circulation. Nevertheless, poisons are slightly 

 and slowly absorbable by the lacteals, especially poisonous salts in a 

 state of solution. The lacteals also absorb innocuous saline matters, 

 sugar, and extractive matters, but not so easily as the veins ; neither 

 do they so readily take up odorous substances; with regard to soluble 

 coloring matters, turmeric is taken up by them, whilst other dissolved 

 coloring substances, such as madder-lake, indigo, gamboge, and rhu- 

 barb, are said not to be absorbed. (Tiedemann and Gmelin.) Sub- 

 stances in a state of extremely minute subdivision, such as charcoal, 

 sulphur, and even particles of indigo, have also been found in the 

 lacteal vessels, as well as in the bloodvessels, having probably pene- 

 trated into those vessels in the villi. 



From the preceding facts, it would seem that the absorbing power 

 of the veins is general, whilst that of the lacteals is select. The veins 

 permit the entrance into them indifferently, of probably all kinds of 

 soluble substances, which do not actually alter or destroy the texture 

 of their coats, but the lacteals have a sort of selective power, by which 

 they take up certain substances in preference to others, nearly, or 

 completely, rejecting some. Both kinds of vessels, but especially the 

 lacteals, appear to allow, in some way or other, the entrance into 

 them of exceedingly niinute particles of insoluble substances, not by a 

 process of dialysis, but by porous diffusion, the pores being, however, 

 invisible in the walls of the capillaries or lacteals, though specially 

 discernible, according to some, in the epithelial cells upon the villi. 

 The direct penetration of the walls of the capillaries and lacteals, has 

 been compared with that of a needle entering a larger vessel. A cer- 

 tain hardness of the penetrating particles is necessary, for lampblack, 

 which is finer and softer than charcoal, does not enter the vessels. 

 Penetration of the soft tissues, by minute bodies, without serious injury 

 to the former, is illustrated by the wandering movements of the smaller 

 Entozoa, through and amongst the living tissues. 



