402 E. T. Bell. 



is apparently not influenced by the fat contained in the other 

 tissues. 



Material and Methods. The material nsed was largely calf foetuses 

 ranging in length from 3 cm. to 105 cm.^ — the latter size l>eing about 

 full term. No data have been obtained as to the relation between the 

 age of the foetus and its length. All descriptions apply to the ox 

 unless otherwise stated. Considerable material from steers in dif- 

 ferent stages of fattening has been made use of. 



For the study of the fat in the epithelial and nuiseular tissues 

 the material was usually fixed in 20 per cent formalin.^ This fixative 

 makes the tissue very firm so that free-hand sections may be made 

 sufiiciently thin for some purposes. Usually, however, frozen sec- 

 tions were made with a Bardeen freezing microtome. The sections 

 were stained in a saturated solution of Scarlet red or Sudan in 

 70 per cent alcohol. In using Scarlet red it was found advantageous 

 to adopt Traina's suggestion (86, pg. 10) of keeping the solution 

 with excess of Scarlet red on the top of an ordinary paraffin oven 

 (this gives about the temperature recommended) for about! two 

 weeks before using. Precipitates are formed less readily from a 

 solution prepared in this way. The stain was filtered each time 

 before it was used. The sections were covered while staining as 

 a slight evaporation of the alcohol is sufficient to cause the formation 

 of a precipitate. After having been stained, the sections were washed 

 in 70 per cent alcohol and then put in water. If they are washed 

 in water directly, a precipitate may be formed by dilution of the 

 alcohol. Of course, the presence of a precipitate makes the detec- 

 tion of fine fat droplets difficult or impossible. By taking the above- 

 mentioned precautions I was able to exclude precipitates as a source 

 of error. 



There are only a few minor differences in the staining powers of 

 Scarlet red and Sudan. When only large droplets of fat are to be 

 stained, Sudan has the advantage in that it acts more rapidly ; but 



'The erowu-rump measurement is meant. 



"Frozen sections were also made ocoasionaUy from material fixed in Zenker'.s 

 fluid, Gilsou's fluid, SO per cent, alcohol, and 10 per cent, formalin. 



