PHYSICAL AND VITAL PROPERTIES OF TISSUES. 43 



secretions as pus. In the inflammatory process they are developed 

 in great quantities; and even the malignant growths, such as cancer 

 and fungus hsematodes which infest the body, owe their development 

 to the same agencies. In short, the nucleated cell is the agent of 

 most of the organic processes, both in the plant and animal, from the 

 time of their earliest development, to their full maturation and decline. 



PHYSICAL AND VITAL PROPERTIES OF THE TISSUES. 



The tissues present manifest differences among themselves, not 

 only in their anatomical structure, but in their properties. These pro- 

 perties maybe divided mio physical and mtal. The physical SiVe 

 those which are dependent solely on the peculiar arrangement or 

 mode of cohesion of the constituent particles of the tissues as well as 

 upon their chemical constitution, and are found as distinctly in the 

 dead as in the living texture. The vz^a/ properties are those which exist 

 only during the life of the organism, and which cease whenever 

 molecular life departs. 



The most striking of the physical properties, are elasticity , flexi- 

 bility, extensibility, ^uA porosity. 



Elasticity is that property by which a tissue reacts, after a stretch- 

 ing or compressing force has been withdrawn. It is strongly marked 

 in the yellow ligament constituting the ligamenta subflava, which is 

 as elastic as India rubber. It is also seen in the middle coat of the 

 arteries, and in the cartilage of the ribs, and on the articular faces 

 of the bones. 



Extensibility is implied in elasticity ; but there are some tissues 

 which are extensible, but not elastic ; such yield only to a long-con- 

 tinued distending force ; of this, we have an example in the resist- 

 ance offered by a fibrous membrane to the growth of a tumour. 



Flexibility is seen in the white fibrous tissues, which are flexible, 

 without being either extensible or elastic. We have examples of this 

 property in the tendons. 



Porosity. The property of permeability by fluids, is possessed by 

 the tissues even after death, and is termed porosity, or imbibition. 

 Animal tissues owe their softness to the watery fluids which they 

 contain, and which fill their pores. 



If a solution of any salt, or of sugar, is poured into a glass tube 

 closed below by a piece of bladder, the particles of the solution per- 

 meate the pores of the bladder, but do not pass through it. If the 

 tube thus filled is placed in a vessel containing distilled water, the 

 fluid gradually rises within the tube, and sometimes to the extent of 

 several inches, while, at the same time, it is found that a portion of 

 the solution has passed from the interior of the tube to the water 

 external to it. 



Dutrochet has named the phenomena above described, endosmose 

 and exnsniose. The term endosmose, or vmbibition, being applied 



