THE CELL DOCTRINE. 103 



vesting membrane of the leucocytes disappear, the 

 granules dissolve and are reabsorbed. 



Capillaries.— The finest capillaries are anatomical 

 elements of tubular form, with transparent resistant 

 walls which measure .001 mm. (.00003937 of an inch) 

 in diameter. These walls contain granular ovoid 

 nuclei, which project, sometimes exteriorly, some- 

 times upon the inner surface of the tubes. These 

 nuclei measure .006 mm. (.00028022 of an inch) in the 

 transverse, and .008 mm. (.00031596 of an inch) in 

 the long diameter. Their long axis is parallel to 

 that of the vessel. The finest capillaries have a 

 diameter of .007 mm. (.0003756 of an inch), leaving 

 a calibre (after deducting the walls) of .005 mm. 

 (.00019685 of an inch), or .002 mm. (.00007874 of an 

 inch) less than the average diameter of the blood- 

 globules Avhich traverse them. 



They are formed as follows : 1st. In new tissues, 

 hollow projections push out from contiguous capil- 

 laries, which meet and unite together. 2d. A solid 

 filament forms, in which nuclei make their appear- 

 ance. Subsequently, the filament becomes hollow, 

 and its nuclei remain the nuclei of the capillary. 



A single perusal of these views as thus illustrated, 

 will convince the reader that spontaneous formation is 

 the prevailing mode of origin of the elements of 

 tissues, according to the French school. Such pe- 

 rusal cannot fail to convince the reader also of the 

 accuracy of description of the fully formed elements 

 described by Robin. 



