TISSUES OF THE BODY. 135 



But while the cells of lymph and chyle are everywhere alike, the con- 

 trary is the case with the remaining elementary particles of these fluids. 



On microscopical examination the chyle of mammiferous animals dis- 

 plays a certain amount of turbidity the cause of its white colour to the 

 eye produced by innumerable minute dust-like particles suspended in it, 

 and not by small globules of fat with which this fluid was formerly sup- 

 posed to be so richly filled. These particles (as is usually the case with 

 substances in a minute state of division suspended in fluid), are engaged 

 in a peculiar tremulous or restless movement, termed the molecular motion 

 of Brown. The more opaque and milky the chyle appears, the more nume- 

 rous are these molecules found to be. They decrease in number again 

 in the larger passages of the lymphatic system, and are completely absent 

 in the clear lymph of fasting animals. Eventually these particles flow 

 from the absorbents into the blood through the ductus tkoracicus, and 

 may form in it transient constituents of the plasma. As to ascertaining 

 their magnitude, with any approach to accuracy, we must confess our 

 utter inability to do so, owing to their extreme minuteness. 



These dust-like molecules consist, we are told by H. Muller, of neutral 

 fats enclosed in a wondrously delicate layer of a coagulated protein 

 substance (albumen). Owing to this they do not coalesce, as free fat 

 globules would do, nor do they on the addition of water. But if chyle 

 be evaporated to dryness, the particles do unite on the subsequent addi- 

 tion of water, as also when acetic acid is mixed with the fluid. They are 

 dissolved by ether, to the action of which the albuminous envelope seems 

 to present no obstacle. We will see further on that these fatty particles 

 represent the fats of the food absorbed from the intestinal tract. 



Besides these, larger and less clearly defined elementary granules of 

 0'0002 - O'OOll mm. in size are to be found in the chyle, partly scattered 

 and partly in groups. They appear to be the wreck of lymph corpuscles, 

 and probably occur in the blood also ( 64) (Hensen, H. Muller). 



Finally, we have blood corpuscles again brought before us in both 

 lymph and chyle. Some of these, doubtless, gain access to our prepara- 

 tions from wounded blood-vessels, and the admixture may be completely 

 avoided by careful dissection. On the other hand, such red cells may be 

 found almost always in the ductus thoracicus of many animals, as, for 

 instance, in that of the dog. The lymph of the spleen further appears to 

 be very rich in red cells (Thomsa), as also that of the liver (Hering}. 

 From this there would appear to be but little doubt that in isolated cases 

 lymph-corpuscles may undergo transformation into red cells before enter- 

 ing the* circulation. For my own part, I believe, I have observed inter- 

 mediate forms in the thoracic duct of the rabbit, between the two species 

 of cells; they are also to be seen in the blood of the splenic vein ( 76), 

 and in the medulla of bones. On the other hand, the possibility of a 

 migration of red cells from the blood-vessels into the lymphatics through 

 the walls of the former ( 81), Hering, must be allowed. 



84. 



!N r ow, the question as to the source of these lymph and chyle cells, is 

 one of the utmost importance for the histology of the present day. 



And since their spontaneous generation in both fluids could not any 



longer be allowed, and that they were found to be either entirely absent, or 



only to occur with extreme rarity in the commencement of the absorbents, 



while immediately after the passage of the fluid through the lymphatic 



10 



