40 GENERAL ANATOMY OF THE TISSUES. 



The changes of the cell-contents are of two kinds, formative 

 and resolvent. Both processes are easily followed in the 

 embryos of different animals, in which, in the first place, the 

 primary formative cells, which at the beginning are distended 

 with the elements of the yelk, especially with oil, acquire by 

 degrees more fluid and homogeneous contents, the yelk 

 granules dissolving, sometimes from the cell-membrane towards 

 the nucleus, sometimes from within outwards ; and secondly, in 

 cells thus formed, the most various new formations take place, 

 among which that of hsematin, of different kinds of pigment, 

 and of fat, are the most obvious. But metamorphoses of the 

 cell-contents are very common in adult animals also, and are at 

 the same time very important, since in many places, on account 

 of the great number of cells which are affected in the same 

 way at the same time, unexpectedly great results are produced, 

 as one of the most important of which we may name the biliary 

 secretion, which is brought about, so to say, only by the 

 activity of the many millions of cells which form the liver. A 

 pretty series of changes may also be traced in the fat cells, 

 which, according to the deficiencj* or superfluity of nutritive 

 fluid, in the one case lose their proper contents, and may even 

 become cells containing mere serum, in others are filled to 

 bursting with drops of oil; again, in the cells of the fat- 

 secreting glands, which at first contain but little fat, and 

 finally become crammed with it ; and also in the lymph- 

 corpuscles, which develope the colouring matter of the blood 

 within themselves, and thus become blood-corpuscles. 1 The 

 formation of mucus, again, must probably be assigned to the 

 epithelial cells of the mucous glands and mucous membranes ; 

 that of the so-called pepsin to the cells of the gastric glands ; 

 and that of semen to the spermatic cells. A multiplicity of con- 

 firmatory evidence is afforded by comparative anatomy, and I will 

 here only advert to the development of the concretions of uric 

 acid in the renal cells of the mollusca, that of sepia in the cells 

 of the ink bag of the Cephalopod, of crystals and concretions 

 of different kinds, in the cells of the iuvertebrata, and of certain 

 pigments in those of the mollusca. Pathological anatomy affords 

 us the pigment formations, the metamorphoses of cells contain- 

 ing blood-corpuscles and the fatty deposits in cells of all kinds. 

 1 [hi the oviparous vertebrata. — Eds.] 



