Histogenesis of the Adipose Tissue. 421 



These figures show beyond doubt that the renal preadipose tissue 

 is a fibrillar connective tissue. It cannot, therefore, be regarded as 

 a special tissue in Toldt's sense distinctly different from ordinary 

 fibrillar connective tissue.^" 



The renal preadipose tissue is not developed from the original 

 protoplasmic mesenchyme. Before any trace of the renal preadipose 

 tissue is to be seen the tissue around the kidney is already differ- 

 entiated into a fibrillar tissue similar to that shown in Textfigiire 

 2 (fc). The structure and development of this tissue has been de- 

 scribed by Mall (22 a). The preadipose tissue develops from this 

 fibrillar tissue and the lobule seems to grow to a large extent by the 

 transformation of this tissue on its periphery. In the early stages 

 the preadipose lobule is not sharply marked off but passes gradually 

 into the adjacent fibrillar tissue. 



One very interesting fact, which has not been called attention to 

 by other observers, is that the branched cells of the preadipose lobule 

 may contain fat droplets long before any true adipose tissue is present. 

 The development of groups of rounded fat cells, such as shown in 

 Text Fig. 4, seldom begins in the renal preadipose before the 30 

 cm. stage ; but fine fat droplets were observed in the cells of the renal 

 preadipose as early as the 14 cm. stage. By staining frozen sections 

 with Scarlet red I have found considerable numbers of fine fat 

 droplets in the renal preadipose cells of three specimens 14 cm., 

 lY cm., and 20 cm. long respectively. In a 24.7 cm. specimen 

 whole lolniles were found where practically every cell contains one 

 or more coarse or fine fat droplets (Plate II, Fig. 7). The cells 

 containing fat occur in all parts of the lobule and have no special 

 relation to the blood vessels. In none of the four specimens just 

 mentioned was there any adipose tissue ]n'esent. They were all 

 in stages such as shown in Text Figs. 2 and 3. The preadipose cells 

 are evidently well along in their differentiation toward true adipose 

 cells. 



'"Of course Toklt did not examine this li^ind of preadispose tissue. He exam- 

 ined only the solid primitive organs of the rabbit, cat, etc. It would be 

 interesting to know if connective-tissue fibrillse are present in the mesen- 

 chyme out of which these organs are developed. 



