82 PHYSIOLOGY AT THE FARM. 



that is to say, the minute vessels into which the arterial 

 branches subdivide most commonly form a network or 

 plexus, while from the same plexus the capillary veins take 

 their origin. The capillary blood-vessels do not undergo any 

 further division. Though not absolutely of the same calibre 

 even in the same part of the body, they are pretty nearly alike. 

 They have no open mouths, as was formerly supposed. Hence 

 whatever fluid escapes from them exudes through their coats, 

 while whatever has not exuded passes on to the venous capil- 

 laries, and returns through veins successively joining into 

 larger and larger branches till it reaches the right side of the 

 heart. The exudation from the capillaries for the purpose of 

 nutrition is the blood-plasma, called the liquor sanguinis 

 namely, the serum of the blood holding fibrine in solution ; 

 while the red corpuscles are retained in the capillaries to be 

 sent back by the veins to the heart. 



The great law of increment or growth in organic nature is, 

 that assimilable matter being brought into contact with a liv- 

 ing texture, that living texture (be it a cell or other form of 

 living tissue) attracts to itself the assimilable material, and 

 undergoes an augmentation. Here the blood-plasma poured 

 forth from the capillary blood-vessels is the assimilable matter. 

 It is in contact with textures of the living frame standing in 

 need of repair. Each living texture attracts to itself from the 

 blood-plasma the materials necessary, in the due proportion 

 and of the due character, to renovate itself after the losses 

 which it has sustained by the disintegration of its own sub- 

 stance in the acts of life assigned to it. A more minute de- 

 tail of the process of repair is not yet afforded by the progress 

 of animal physiology. It is, nevertheless, strictly in accord- 

 ance with the law known to pervade all organic nature. Thus 

 the simplest form of nutrition and growth, as in the red snow 

 (an isolated vegetable existence consisting of a single cell), is 



