OP THE VEINS. 295 



any muscular fibres whatever. A minute artery 

 which is not more than the 2 J O th of an inch in 

 diameter, exhibits well defined muscular fibre cells, 

 which encircle it closely and regularly, but upon 

 many a vein which is as much as the -^th of an inch 

 in diameter, I have not been able to demonstrate one 

 single muscular fibre cell. The walls seem to be 

 entirely composed of very delicate connective tissue 

 with which are connected oval masses of bioplasm in 

 immense numbers. These are sometimes so closely 

 placed as almost to touch one another. This im- 

 portant fact may be demonstrated very readily in the 

 small veins of the pia mater if they are properly pre- 

 pared with the carmine fluid Plate XV, fig. 2. The 

 observer will be astonished at the great number of oval 

 bioplasts in the walls of the small veins, as well as in 

 the capillaries near the veins. These bioplasts have 

 not, I think, been figured or accurately described, nor 

 has attention been drawn to the very important 

 offices they probably fulfil in connection with physio- 

 logical changes that are constantly going on as long 

 as life lasts. It must be obvious that bioplasts dis- 

 tributed in such number as are those in the wall of 

 the small veins, perform other functions besides 

 taking part in the formation of the tissue of the 

 vein. As I have already endeavoured to show the 

 activity of change in an organ or texture, may be 

 judged of by the number of bioplasts present in it. 

 In veins the bioplasts are many times as numerous as 

 would be required to produce the very small, amount 

 of tissue entering into the formation of their coats. 

 The blood in these small veins undergoes important 

 changes, just as it does in the capillaries, and the 

 agents concerned are the bioplasts. In short, physio- 

 logically, the small veins may be considered as part 

 of the capillary system, and concerned in nutrition* 

 and in the removal of products of disintegration re- 

 sulting from changes in the tissues. 



