576 Comparative Physiology. 



is improper and insufficient, when applied to mean the elabo- 

 rated sap, proper juice, or nutritive fluid of plants, which they 

 have too generally been. It is clear, also, if we adopt the idea, 

 that the nutritive fluids, capable of serving the general purposes 

 of the plant, circulate through such capillary vessels, then there 

 must be other similar vessels in these plants containing those 

 nutritive fluids, which may hereafter be found to be the case. 

 The nutritive fluid must contain carbon, hydrogen, and oxygen, 

 in something near the proportions required to form the system 

 in general ; to vfhich mucilage seems to be the nearest approxi- 

 mation of any of the organisable or proximate products. It 

 must also contain nitrogen, indispensable in the formation of all 

 new matter, besides being assimilated by many of the organs ; 

 this may be in the state of fibrin or gluten, so easily separated 

 from the vegetable juices, or in the state of proteine, the basis 

 of fibrin or gluten, albumen, and caseine, which differ only in 

 their saline earthy ingredients. The nutritive fluid must also 

 contain the saline earthy ingredients required for so many of 

 the organic products. The cambium, the main product of the 

 elaborated sap, is principally composed of mucilage. The muci- 

 laginous juices have not been so much submitted to analysis as 

 the milky juices ; but the analysis of mucilage of lintseed, given 

 Vegetable Chemistry, p. 674., shows their fitness for the purposes 

 of general nutrition. It contains, besides 7*11 per cent of ashes 

 of saline matter, the following proportions of organic, viz. : — 



Carbon - - - 34-30 



Hydrogen - - - 5-65 



Oxygen - - - 52-78 



Nitrogen - - - 7-27 



100 



The excess of hydrogen and oxygen above carbon is owing 

 to the mucilage containing 10 per cent of water, which is pro- 

 bably contained in tissue in a free state. Miiller says all the 

 animal tissues contain j of water in a free state, and, if this be 

 pressed out, they cannot live. Seeds also contain free water, 

 and, if this be dried up, they die. Water seems necessary to pre- 

 serve the capability of living in the tissue. 



From juices of this description the general products of the 

 system might be formed ; and if mucilaginous juices similar to 

 the above are found by subsequent observation to circulate 

 in masses of capillary vessels similar to the laticiferous, and in 

 sufficient quantity to furnish a channel for the general current, 

 we may then adopt the opinion that the general circulation 

 passes through vessels of this description. If not, we must resort 

 to the old opinion, that such products are peculiar secretions 

 circulating in peculiar vessels, and not the general channel of 

 circulation as supposed by Dr. Carpenter. 



Besides the assistance of gravitation, vibration, contractility. 



