Histogenesis of the Adipose Tissue. 415 



tive organs) lose their processes and become rounded or polygonal 

 before the deposit of fat begins. This distinction was based on the 

 study of animals like the eat in which the primitive organs are com- 

 posed of i)olygonal cells rich ill protoplasm. 



liammar (1-i) made a comprehensive and thorough study of 

 adipose tissue and acquired a deep insight into the subject. He 

 agrees with Kolliker that all adipose cells are ultimately derived 

 from fixed connective tissue cells. The primitive organs are formed 

 from branched mesenchymatous cells. He distinguishes primary 

 and secondary adipose tissue-formation. By the former he means 

 those instances where the tissue is formed into well defined lobules 

 (primitive fat organs) before fat impletion begins; by the latter 

 he means the formation of adipose tissue without primitive organs. 

 In primary adipose tissue-formation the cells may develop a large 

 amount of protoplasm before the deposit of fat begins (primitive 

 organs of rat, rabbit, cat, etc.) ; or they may begin to accumulate 

 fat without showing any marked increase of protoplasm (primitive 

 organs of calf, man, dog). Hammar's work reconciled the views 

 of Flcmming and Toldt in a very satisfactory and convincing way. 



Hamniar found that the primitive organs of some animals, as the 

 rat and rabl)it, develop at first as compact masses of cells rich in 

 protoplasm. These polygonal cells next accumulate many small fat 

 droplets — the droplets being always separated by protoplasm. In 

 some animals as the rabbit, the small droplets increase in size and 

 finally flow together to form a single droplet, thus producing an 

 ordinary fat cell. In other animals, however, as the rat, the cells 

 persist in the early multiglobular form throughout life. This latter 

 tissue Hammar calls brown adipose tissue. The so-called hibernating 

 gland of some animals has the same structure. 



In man and in the ox Hammar finds primitive fat organs only 

 adjacent to the kidneys. Subcutaneous fat is formed without any 

 preformed lobules. Hammar did not attach any great significance 

 to his classification of primary and secondary adipose tissue- 

 formation. He recognized the possibility of the occurrence of transi- 

 tion forms and even mentions one instance of such in the scalp of 

 a human foetus. As will appear later, my observations show that 



