230 THE SOLIDS. 



This superficial layer of fat is also generally thicker in 

 children and in women than in men. 



Again, there are other peculiar situations in which fat 

 is almost invariably encountered, as in the orbit, in the arti- 

 culations, where it constitutes the glands of Havers, in the 

 shafts of the long bones formifcg the marrow, in the vertebral 

 canal, and in many other localities where vacancies occur 

 which require to be filled up. The marrow differs only from 

 ordinary fat in that the cells composing it are more circular, 

 with but little admixture of cellular tissue. 



On the other hand, there are situations in which, under 

 no circumstances, is fat developed, as in the eyelids, in the 

 axillae, between overlapping muscles, and in the genital 

 organs. 



Quantity. The amount of fat varies greatly in different 

 species of mammalia, in different individuals of the same 

 species, and in the same animal at different times. 



Thus certain animals seem to have a peculiar aptitude for 

 the formation of fat, as the pig. 



Again, the various members of one family are sometimes 

 observed to be remarkable for the constitutional predisposi- 

 tion exhibited to the formation of fat. Again, other families 

 are met with equally remarkable for their indisposition to 

 fatten. 



Lastly, in some animals the fat accumulates at particular 

 periods in greatly increased quantities, as in the hibernating 

 mammalia, and in the larva? of insects. In man the fat 

 usually undergoes an augmentation after the meridian of life 

 has been passed. 



Castration peculiarly predisposes the system to the form- 

 ation of fat. 



Occasionally, also, fat is secreted in vast and abnormal 

 quantities : where this augmentation is general it constitutes 

 the diseased condition of obesity ; and where it is only partial 

 it gives rise to tumours, often of great magnitude. 



In general, a certain degree of fatness argues a healthy and 

 vigorous condition of the system, while its excess or inor- 

 dinate accumulation denotes either a degree of weakness of 



