FAT 



75 



FIG. 77. Cells from fat body of the insect, Regalis. 

 X 580. 



resembles the materials stored in the vertebrate liver. The cells, how- 

 ever, seem to store them as reserve food supplies, as is demonstrated by 

 the fact that before par- 

 ticular growth periods, 

 when the creature will be 

 unable to eat, huge quan 

 tities of these materials are 

 collected in the cells, and 

 when the growth and molt- 

 ing is over they have been 

 used. 



The "fat-bodies" of the 

 insects furnish an example. 

 These bodies are strings of 

 mesodermal cells lying in 

 the body cavity of various 

 larvae. Figure 77 shows a 

 section of such a fat-body 

 from the larva of a Regalis 

 moth. This larva had just 

 completed a molt, and the cells do not therefore show as much food 

 material as they would if the tissue had been taken just before the 

 molt. 



The Crustacea also present analogous tissues that are probably used 

 as stores of reserve foodstuffs, especially just before the molting period. 



Technic. The fats may be cut like any other tissues, and such sections 

 yield very good results, especially when one is already well acquainted 

 with the tissues. To get so acquainted as well as to decide with accuracy 

 if a given vertebrate tissue contains fat or not, the material should be 

 cut fresh with a freezing microtome and the sections stained with some 

 of the specific fat stains, of which there are a number in the list of ana- 

 line dyes. Osmic acid will also stain the fat substance a good black that 

 can be readily recognized. 



LITERATURE 



KOSCHEVNIKOFF, G. A., iQoo. " liber den Fettkorper und die Oenocyten der Honigbiene 



(Apis mellifica)," Zool. Anz., Band XXIII. 

 WIELOWIEJSKI. H. v., 1883. " liber den Fettkorper von Corethra plumicornis und seine 



Entwicklung," Zool. Anz., 1883. VI Jahrgang, pages 318-322 

 Read of the development and structure of human fat in any of the best medical his 



tologies. 



