OF NON-VASCULAR ANIMAL TISSUES. 161 



To the elaborate researches of these physiologists, and to those of Miiller, Valen- 

 tin, PuRKiNjE, Henle, &c., I must refer for information upon the nature and intimate 

 structure of these corpuscles. 



These cells are modifications of two principal forms, the one being either round or 

 oval, the other compressed in the form of a scale ; and their existence in one of these 

 two forms has lately been detected in most organs of the body. 



In a circular form they appear to be the principal components of bone, cartilage, 

 muscular and nervous fibre, and of the parenchyma of glands*; in the form of a 

 flattened cell or scale, they constitute the epidermis and its appendages, the epithe- 

 lium of mucous and serous membranes, and of the inner tunic of the vascular 

 system. 



When the almost universal presence of these cells is considered, I think it cannot 

 be doubted but that they perform important parts in the functions of nutrition and 

 secretion. 



I am induced to agree with M. Schwann, that these cells have vital actions, and I 

 believe that they not only possess them in the tissues during development, but also 

 in subsequent periods of life. I ascribe to them the function of circulating, and of 

 perhaps changing the nature of, the nutrient fluid which is brought to the circum- 

 ference of the solid non-vascular tissues, and I believe them in some measure to 

 compensate for the absence of the internal vascularity possessed by other struc- 

 tures. 



In proof that they possess vital properties, I may allude to the changes undergone 

 in the structure of the cornea and the crystalline lens, without the penetration of 

 them by any vessels. 



I must here observe, that in some of the non-vascular tissues, as in the cornea 

 and the vitreous humour, where only a small quantity of corpuscles exists, the 

 laxity of their consistence admits of their ready penetration by the nutrient fluid 

 brought to their circumference. 



The only difference which appears to me to exist between the mode of nutrition in 

 the vascular and the non-vascular animal tissues is, that the former derive their nu- 

 trient fluid from the blood which circulates through the capillaries contained in their 

 substance ; and that the latter are penetrated by the nutrient fluid which exudes 

 from the large vessels by which they are surrounded, and that its distribution 

 through them is assisted by the vital properties of the corpuscles which they con- 

 tain ; in both classes, the particles of which the tissues are composed attract from 

 this fluid the elements which nourish them-j~. 



Journal, and to some additional pages by Dr. Baly, in the second edition of his Translation of Muller's Ele- 

 ments of Physiology, that I am indebted for my knowledge of Schwann's and Schleiden's labours. 



* Valentin and Pubkinje. 



t In reference to this subject, I beg to direct particular attention to the following quotation from Professor 



