60 MATERIAL COMPOSITION OF MAN. 



The blood, chyle and lymph. Bone or osseous tissue. 



Epidermic tissue, including epi- Muscular tissue. 



thelium, cuticle, nails, and Nervous tissue. 



hairs. Bloodvessels. 



Pigment. Absorbent vessels and glands. 



Adipose tissue. Serous and synovial membranes. 



Cellular (areolar) tissue. Mucous membranes. 



Fibrous tissue. Skin. 



Elastic tissue. Secreting glands. 

 Cartilage and its varieties. 



Under the idea, now entertained, that all organized tissues are essen- 

 tially composed of cells having plastic or formative powers, with an 

 intercellular substance or blastema, the tissues have been thus arranged 

 by Schwann, 1 the great author of the cell doctrine. 



1. Isolated, independent cells. To this class the cells in fluids pre- 

 eminently belong : lymph globules ; blood corpuscles. 



2. Independent cells united into continuous tissues; such as the horny 

 tissues and the crystalline lens. 



3. Cells in which only the cell walls have coalesced, cartilage, bone, 

 and the substantia propria (ivory) of the teeth. 



4. Fibre cells, cellular (areolar), fibrous and elastic tissue. 



5. Cells in which both the cell walls and cell cavities have coalesced, 

 muscle, nerve and capillary vessels. 



Dr. Allen Thomson 2 has proposed the following tabular view, which 

 he remarks may be adopted in preference to the foregoing as com- 

 bining similar theoretical considerations, with a more immediate refer- 

 ence to the actual form of the prevailing structural elements in the 

 different tissues. He properly adds, however, that this classification is 

 open as he might have said every arrangement must be to several 

 objections ; inasmuch as it brings together, under the same head, some 

 parts endowed with different functions ; and separates some tef tures 

 whose functions are closely related ; and it does not point out suf- 

 ficiently the usual degree of complexity of the several textures. 



Some part of it, moreover, is founded on theoretical considerations 

 not yet fully established ; and the* distinctions on which it rests are 

 based on a structural analysis of various extent in the different textures. 

 On the whole, however, it is a sufficient exponent of the existing state 

 of belief on the subject. 



I. Organized textures in which the cellular form of the constituent 

 elements is apparent; not unfrequently also presenting granules of 

 molecular deposition. 



1. Rounded simple cells, floating loose in fluid, Blood, Lymph, Chyle 

 and Milk corpuscles, $c. 



2. Simple cells massed together, either preserving their cellular form, 

 and without other parts intervening, or altered in form and mixed with 



1 Microscopical Researches into the Accordance in the Structure and Growth of Animals 

 and Plants. Sydenham Society's edit., by Henry Smith, p. 66, London, 1847. 

 3 Outlines of Physiology for the Use of Students, pt. i. p. 68, Edinb., 1848. 



