68 ANATOMY. 



capillaries. Nucleated cell-tissues are represented by the white and 

 early stage of the red blood-corpuscles, by the epithelial and epidermic 

 cells, the pigment cells, the cells of the adipose tissue, and by the gan- 

 glionic corpuscles of the gray nervous substance. A nucleated cell is said 

 to consist of an outer part or periplast, and certain contents, named the 

 endoplast, lying in which is a nucleus, and within that, often, a nucleolm, 

 or nucleoli: sometimes the periplast or envelope is indistinct or absent ; 

 and the entire cell may be soft, or firm, or even dry. Nucleated cells 

 having an envelope, such as the epithelial cells and red blood-cells, 

 might be conveniently termed eystopla&ts ; whilst the naked cells, 

 without envelopes, such as the white blood-corpuscles, might be named 

 gymnoplasts. The nuclei of these cells, and those found in the con- 

 nective and muscular tissues, are regarded as nutritive centres, sur- 

 rounded by protoplasm or germinal matter. Nucleated cells, embedded 

 in solid blastema, occur in cartilage and in bone. Ramified or branch- 

 ing cells with nuclei, form the so-called connective tissue corpuscles. 

 The fibres of the areolar, fibrous, and elastic tissues, are usually said 

 to be produced by the fibrillation of intercellular substance. Mixtures 

 of such fibres, with cartilage cells, form the white and yellow fibro- 

 cartilages. Nucleated cells, elongated, perhaps joined, and composed 

 of a peculiar substance, form the unstriped muscular fibres, and the 



fray or gelatinous nerve-fibres of the sympathetic system. Compound 

 bres, themselves derived from the union and modification of several 

 nucleated cells, occur in the highly organized striped muscular fibres, 

 and in the white or tubular nerve-fibres. Lastly, the commencing 

 lymphatic vessels, and the capillaries, are examples of tubular tissues 

 derived from the junction of ramified nucleated cells. The larger 

 bloodvessels and lymphatics, and the ducts of glands, are really com- 

 pound structures, or organs, built up of several tissues : so too, of 

 course, are the various membranes, the glands and the organs of the 

 senses, and such large organs as the brain, heart, and lungs. 



Size of the Structural Elements of the Tissues. 



Perhaps the best practical notion may be formed of the extremely 

 minute size of the objects we have just been considering and describ- 

 ing, by reflecting on the statement that the red blood corpuscles of 

 man are on an average ^^oth of an inch in diameter, and about Jth 

 of that or y^J^^th of an inch in thickness: in other words, 3300 of 

 these little bodies placed side by side would occupy one inch in 

 length, and 13,000 piled one on the other would stand just an inch 

 high. About 1300 red corpuscles would be necessary to cover the 

 dot of this letter, i, and upwards of ten millions to cover a square 

 inch of paper. A cubic centimetre, or yj^ths of a cubic inch, of 

 human blood contains upwards of 5,000,000 of red, and 14,000 of 

 white corpuscles. (Vierordt.) The red blood corpuscles may be taken 

 as a rough standard of comparison in measuring all the other micro- 

 scopic objects met with in the tissues ; but these corpuscles vary in 

 size, even in the same person, some being as much as a third larger or 

 smaller than the average. The following is a list of the chief objects, 



