298 PHYSIOLOGY CHAP. 



or stomata, or permit the occasional formation of clefts in the lines 

 of junction, through which the minute fat droplets can pass easily. 

 It must, however, be stated that in chyle the fat is found in 

 a highly fractional form (sometimes known as the molecular 

 basis'), while in the cytoplasm of the columnar cells, and also in 

 the adeuoid reticulum that surrounds the central lacteal, it appears 

 in the form of globules of various sizes. We are ignorant of the 

 mechanism by which this extremely fine division and conversion 

 of the fat emulsion into the molecular basis of chyle takes place, 

 but it seems reasonable to suppose that it occurs at the moment 

 of passing into the lacteal, i.e. that the fat globules are altered 

 and broken up in penetrating through the very fine pores that 

 exist or are formed between the junctions of the epithelioid cells. 



Hofmeister's notion that the leucocytes which accumulate in 

 the villi during absorption convey the fat into the lacteal must, 

 as already stated, be abandoned. Two facts in particular tell 

 against it. After administration of magnesium sulphate, which 

 produces a cathartic effect, i.e. opposed to absorption, an extra- 

 ordinary number of leucocytes accumulate in the villi, although 

 there is not and cannot be any fat absorption. On the other hand, 

 they are entirely absent from the villi of a sucking puppy, 

 although there is a marked passage of fat into the chyle (Foster). 



It is evident that great importance in the penetration of fai 

 into the lacteals attaches both to the passive compression of the 

 villi due to the peristaltic movements of the intestine (Hamburger), 

 and to the active movements of the villi induced by the (probably 

 rhythmic) contraction of the muscle cells, with which the areolar 

 tissue of the villi is well provided. According to Briicke, the 

 muscles of the villi act during contraction like a pressure pump, 

 which empties the contents of the lymph spaces of the stroma into 

 the central lacteal, and the latter into the subjacent lymphatics, 

 which are provided with valves. The valves hinder a reflux 

 during the subsequent relaxation or expansion of the muscles, and 

 thus indirectly allow the lymph sinuses to refill with new material 

 absorbed and secreted by the columnar epithelial cells. Since the 

 muscle bundles have a direction predominatingly parallel to the 

 long axis of the villi, Briicke supposes that during contraction 

 the villi shorten and empty by positive pressure, while during 

 relaxation they lengthen and expand by negative pressure. But 

 it is possible to conceive the mechanism differently. According 

 to Heidenhain the villi shorten and thicken during contraction, so 

 that the central lacteal dilates. During relaxation the villi 

 lengthen and become thinner, in consequence of which the central 

 lacteal is constricted by compression, and evacuated. However we 

 conceive of the phenomenon, it is certain that a rhythmical con- 

 traction and expansion of the villi must favour (if it does not 

 absolutely initiate) the movement of the regenerated products 



