27. The term SYSTEM is applied to an assemblage of organs arranged according to some plan, or method; as the nervous system, the respiratory system. -=-=-=-=-=-=-=-=-=-=-=-= 22. Define a fibre. 23. Define a fasciculus. 24. Define a tissue. 25. Define an organ. What is the action of an organ called? Give examples. _Mention other examples._ 26. What is an apparatus? Give an example 27. How is the term system applied? -=-=-=-=-=-=-=-=-=-=-=-= 28. A TISSUE is a simple form of organized animal substance. It is flexible, and formed of fibres interwoven in various ways; as, the cellular tissue. 29. However various all organs may appear in their structure and composition, it is now supposed that they can be reduced to a few tissues; as, the _Cel´lu-lar_, _Os´se-ous_, _Mus´cu-lar_, _Mu´cous_, _Ner´vous_, &c. (Appendix B.) 30. The CELLULAR TISSUE,[2] now called the _areolar tissue_, consists of small fibres, or bands, interlaced in every direction, so as to form a net-work, with numerous interstices that communicate freely with each other. These interstices are filled, during life, with a fluid resembling the serum of blood. The use of the areolar tissue is to connect together organs and parts of organs, and to envelop, fix, and protect the vessels and nerves of organs. [2] The _Cellular_, _Serous_, _Dermoid_, _Fibrous_, and _Mucous tissues_ are very generally called _membranes_. [Illustration: Fig. 3. Arrangement of fibres of the cellular tissue magnified one hundred and thirty diameters.] -=-=-=-=-=-=-=-=-=-=-=-= 28. What is a tissue? 29. What is said respecting the structure and composition of the various organs? Name the primary membranes. 30. Describe the cellular tissue. How are the cells imbedded in certain tissues? Give observation 1st, relative to the cellular tissue. -=-=-=-=-=-=-=-=-=-=-=-= _Observations._ 1st. When this fluid becomes too great in quantity, in consequence of disease, the patient labors under general dropsy. The swelling of the feet when standing, and their return to a proper shape during the night, so often noticed in feeble persons, furnish a striking proof both of the existence and peculiarity of this tissue, which allows the fluid to flow from cell to cell, until it settles in the lower extremities. 2d. The free communication between the cells is still more remarkable in regard to air. Sometimes, when an accidental opening has been made from the air-cells of the lungs into the contiguous cellular tissue, the air in respiration has penetrated every part until the whole body is so inflated as to occasion suffocation. Butchers often avail themselves of the knowledge of this fact, and inflate their meat to give it a fat appearance.