4 H. HAYS BULLAKD 



erence mainly to skeletal nm-scle but we both stated that our 

 results also applied to cardiac muscle. Wegelin ('13), working 

 independently, obtained experimental results similar to those 

 which Bell and I had previously published. Wegelin gives one 

 drawing showing fat in the heart muscle of a normal rat. With 

 this single exception there are, in the literature, no figures pur- 

 porting to show the normal fat content of cardiac muscle. 



In the recent literature are two important communications, 

 by Eyselein ('14) and Borchers ('14). Both of these authors 

 are familiar with the work of Wegelin but neither is able to 

 confirm his results. In general, the observations recorded in 

 the present paper are in agreement with those of Hofbauer 

 ('05), Bell ('11-'12), Wegelin ('13), and with my own previous 

 work ('12-'14). 



I am indebted to Prof. R. E. Sheldon for kind encouragement 

 and valuable criticism in connection with the work of this paper. 

 In making the figures I have received a number of helpful sug- 

 gestions from Miss S. E. Watson, artist of the Department of 

 Anatomy. 



METHODS 



Technique oj fat demonstration. In the demonstration of fats 

 in tissue sections, methods and technique are of the utmost im- 

 portance. The wide divergence of opinion among different in- 

 vestigators concerning the occurrence of fat within the cells of 

 normal and of pathological tissues is due primarily to differences 

 of technique in preparing the sections for examination. I have 

 elsewhere ('12 b) treated this subject in some detail and shall 

 here give only a brief outline. 



Fixation. Fat containing material is usually fixed in formalin. 

 Bell ('11) and Bullard ('12) have pointed out that this fixative, 

 although frequently giving excellent results, is not to be relied 

 upon under all circumstances. Frozen sections of the heart or 

 other tissues which have been fixed in formalin may, when care- 

 fully stained (Scharlach R.), appear to contain little fat, while 

 sections of the same material when stained fresh without previous 

 fixation may be loaded with droplets. This apparent disappear- 



