H. MUNRO FOX 571 



comes to rest in contact with the 'Ventral gills," the first appearance of 

 oxyhemoglobin is inside the abdominal segment nearest to the bubble 

 and not within the "gills" themselves. This fully bears out the result 

 obtained with the flagellates. Whatever be the function of the "ven- 

 tral gills," it is not that of absorbing oxygen. 



The spectroscopic method is one suited to this particular larva 

 alone; it cannot be applied where hemoglobin is absent. The flagel- 

 late method, however, is one of general application. 



At the same time that the oxygen intake was studied, the relative 

 output of carbon dioxide by different surfaces of the body was inves- 

 tigated. This was done by mounting the larva on a slide in the same 

 manner as for studying the oxygen absorption, but, in place of a 

 suspension of flagellates, an indicator was used which changes color 

 as carbon dioxide goes into solution, altering the hydrogen ion con- 

 centration of the water. The position and extent of the color change 

 indicates the place and amount of the carbon dioxide output. Sev- 

 eral indicators are available which change in color about the neutral 

 point of water. Neutral red and rosolic acid were tried but were 

 found unsuitable for these experiments because in the thin layer of 

 solution between cover-slip and slide the colors are not sufficiently 

 intense to show a sharp change. The indicator which was found 

 suitable for use was a solution of hematoxylin with just sufficient 

 alkali added to make it a bluish pink. In regions where carbon 

 dioxide is being given off by the larva into the water the bluish pink 

 color changes through orange to yellow. The color change is sharp 

 even in the thin layer of liquid between cover-slip and slide. It 

 can be more exactly observed when the examination is made under a 

 very low power of the microscope, such as a 2 inch objective. All 

 tests were discarded in which the larva defecated or in which any 

 liquid at all came out through the anus, for the rectal fluid is alkaline. 



Using the red Chironomus larva it was found by this method: 

 (1) that carbon dioxide is given off by the whole body surface 

 except by the head and the ventral gills; (2) that most carbon 

 dioxide is given off by the posterior abdominal segments, but that the 

 relative amounts given off by different segments vary in different 

 individuals and in the same individual at different times; (3) that 

 carbon dioxide is not always given off by the different surfaces of an 



