SECT. 13.] CHANGES IN FAT-CELLS. 11, 



pend, whether, as it would appear, the original cell-membrane r in 

 many places, really changes in its composition after a time, or 

 whether, perhaps, the change in the reaction only appears to be 

 founded in the absorption of foreign substances, in the incrustation 

 of the cell-membrane with sails, etc., or whether, as is most proba- 

 bly the case in cartilage-cells, it is dependent upon secondary depo- 

 sitions on the exterior of the primitive membranes. 



The metamorphoses in the cell-contents are of two kinds, forma- 

 tive and resolvent. Both processes can be readily followed in the 

 embryos of different animals, in which, firstly, the primitive cells, 

 distended at the beginning with the elements of the yelk, gradually 

 acquire more fluid and homogeneous contents, the yelk granules 

 resolving sometimes from the cell-membrane towards the nucleus, 

 sometimes from within outwards ; and secondly, in the cells so 

 changed, the most various new formations appear, among which 

 those of haematine, the different pigments, and of fat, are most 

 conspicuous. But even in adults, metamorphoses of the cell-con- 

 tents are common, and, at the same time, very important pheno- 

 mena, occasioning in many places, owing to the enormous number 

 of cells, unexpectedly extensive results ; the secretion of the bile 

 may be characterised as the most important of these, which, so to 

 speak, is effected by the activity of the many millions of hepatic 

 cells forming the liver. 



A beautiful series of changes may also be traced in fat-cells, which, 

 according to the deficiency or excess of nutritive fluid, lose, in 

 the former case, their contents, and may eventually contain only 

 serum, in the latter become distended with fat-drops ; further, in the 

 cells of glands secreting fat, which, at first poor in fat, are ultimately 

 quite distended with it, as also in the lymph-corpuscles, which deve- 

 lop the colouring matter of the blood in themselves, and become 

 blood-corpuscles ; lastly, in the ova of all animals which deposit fat 

 and proteine within themselves. The formation of mucus also must, 

 according to my observations, be considered as taking place in the 

 epithelial cells of the mucous glands and membranes, as also that 

 of pepsine, as it is called, in the cells of the tubular glands of 

 the stomach. Comparative Anatomy can furnish further proofs 

 of the most diverse description ; and I now only mention here the 

 formation of uric acid concretions in the renal cells of Mollusca, 

 that of sepia in the cells of the ink-bag of the Cephalopoda, of crys- 

 tals and concretions of various kinds in cells of invertebrata and of 

 special colouring matters in those of the Mollusca. Very interesting 

 also is the occurrence, in invertebrate animals, of glands consisting 



