PROPERTIES OP THE TISSUES. 65 



another, give way and form continuous tubes, as those of the 

 renal and seminal tubuli. 



In the second case, where the Cell cavity disappears, the 

 parietes of the Cells lie flat together, forming solid laminae, 

 as in membrane. 



The Nuclei of the Cells elongate and coalesce, and form 

 nucleus fibres, which differ from the Cell fibres by being 

 insoluble in acetic acid. 



PHYSICAL PROPERTIES OF THE TISSUES. 



The different Tissues possess the properties of density, 

 color and consistency, as matter in general: some of them 

 also have elasticity and pliability, properties which are due 

 to the presence of water. 



VITAL PROPERTIES OF THE TISSUES. 



The vital properties are termed Contractility, Sensibility, 

 and what is called the Formative force. Contractility mani- 

 fests itself in the shortening of living tissues under the 

 influence of mechanical or chemical stimuli, or the stimu- 

 lus from the nerves, as seen in the muscles. Voluntary 

 contractility belongs to the muscles of locomotion, which 

 contract through the agency of the brain. There is another 

 kind of contraction, permanent in its character, arising from 

 a great degree of heat, and is a sort of crisping not to be 

 confounded with vital contraction. 



Sensibility of the tissues is due to the nerves and their 

 connection with the brain, and the amount of sensibility 

 which any tissue may possess is measured by the number of 

 its sentient nerve fibres. 



The Formative force, called also the Plastic or Assimila- 

 tive force, is that power in the different tissues to form them- 

 selves out of materials altogether unlike those of which they 

 are severally composed; and formation, assimilation, and 

 nutritious processes are terms applied to the working of this 

 power. 

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