HEART-BODY, ETC., OF CERTAIN POLYOH/I^.TA . 279 



become green. It appears, then, that a number of fat globules 

 exist side by side with the granules — a state of things which 

 accords with the effect of ether, mentioned above, of dissolving 

 out fat from the heart-body. This view is clearly confirmed 

 by the use of Soudan III. The reaction of this aniline colour 

 on fat was recently discovered by Daddi [11]. Professor Mayer 

 informed me that he had examined it, and found it appeared 

 to be a reliable stain for all fats, rendering them bright 

 orange. In a hand-section of material fixed in alcohol, and 

 stained on the slide with a solution of Soudan in 70 per cent, 

 alcohol, and then teased in glycerine into fragments, numbers 

 of fat droplets stained a bright orange colour are seen distri- 

 buted in the cells. They are especially abundant in the outer 

 layers. In the heart-bodies of Audouinia that had been about 

 a month in the aquarium tank, fat had entirely disappeared. 



The finding by Guido Schneider of iron naturally occurring 

 in the heart-body of Pectinaria has been mentioned above. 

 I found that in the case of Audouinia, hand-sections of 

 material fixed in alcohol, when laid in ferrocyanide of 

 potash solution, acidulated with hydrochloric acid, showed a 

 blue coloration of the gut wall at once ; but in the heart-body 

 when teased only a few insignificant fragments were bright 

 blue. MacAUum's ammonium-hydrogen sulphide method ^ 

 for micro-chemical detection of iron [21], although it of course 

 shows inorganic and albuminate compounds of iron, is espe- 

 cially designed to reveal iron in higher organic compounds, 

 such as nucleins, which exist, as well as in nuclei, also in 

 secreting cells, yolk of egg, hsematoblasts, and other such bodies. 

 On laying a hand-section of the heart-body in a drop of 50 per 

 cent, glycerine thoroughly mixed with two drops of ammonium- 

 hydrogen sulphide, there was no immediate reaction except a 

 slight general greenish tinge. The tissue was then teased by 

 means of drawn-out glass rods with broken points, instead of 

 needles, and, covered with a cover-slip, was left in a water-bath 



1 Since this work was done MacAUuni has published a new and easier 

 method for the micro-chemical detection of iron, in the ' Journal of Physio- 

 logy,' September, 1897. 



