108 CARNEGIE INSTITUTION OF WASHINGTON. 



in the glandular cells of the stomach, duodenum, and the lower part of 

 the small intestine, the amount varying in the different animals from 

 a trace to large quantities. From these observations it is apparent 

 that the normal presence of fat in these tissues must be taken into 

 account in all future experiments on fat absorption. 



As one of the roles played by the mitochondria, it has been claimed 

 by several observers that they form fat droplets. Mrs. Margaret R. 

 Lewds has devised a method by which she has been able to show that 

 fat droplets unquestionably may form in a living cell without being 

 associated at any time with the mitochondria. To this end she stained 

 egg-yolk with Sudan III and, diluting it with Locke-Lewis solution, 

 placed it on 24-hour cultures of 6 to 9 day chick embryos. Since fat 

 combined with Sudan III, when fed to animals, passes through the 

 intestinal wall and is deposited in the body-cells in the form of red fat 

 globules, we should expect in tissue cultures to find it deposited in the 

 mitochondria before appearing as red fat globules in the cytoplasm; 

 that is, if the mitochondria are fat producers. Such, however, was not 

 the result. Within a few hours after the application of the Sudan III- 

 yolk solution, exceedingly small, reddish-yellow fat droplets appeared 

 in the cytoplasm of the cells entirely distinct from the mitochondria. 

 Some of the orange-colored droplets fused, others appeared in the 

 course of the next few hours, and in time the fat droplets originally 

 present in the cell had taken up the stain until it was impossible to 

 distinguish them from the new ones by their color. At no time did the 

 mitochondria contain orange-colored droplets, nor did they become 

 rounded, looped, or ring-shaped, or show any other supposed tran- 

 sitional forms. 



In my report of last year I described the studies on the growth of 

 cross-striated muscle-fibers in tissue cultures by M. R. Lewis and W. H. 

 Lewis, and also another paper by the same authors on the contraction 

 phenomenon of smooth-muscle cells in hanging-drop preparations of 

 the amnion of the chick. These muscle investigations have been con- 

 tinued by Mrs. Lewis, who has completed a careful cytological study 

 of the development of the heart-muscle in chick embryos of 28 hours 

 to 4 days of incubation. By combining observations on fresh tissue 

 with the study of fixed and stained material, she has discovered impor- 

 tant facts regarding the development of cross-striations and their 

 relation to myofibrils, concerning which there has heretofore been a 

 wide divergence of opinion. The fixed material was prepared as a total 

 mount by treating the blastoderm with a solution of corrosive sub- 

 limate 5 per cent, with the addition of a little osmic acid, and the 

 extension of the heart was secured by the weight of the cover-slip. 

 In such preparations Mrs. Lewis found that within the individual 

 muscle-cell there is a gradual accumulation of some substance which, 

 upon fixation, gives the appearance of fibrils. The type of fibrils into 



