134 



Scientific Proceedings (113). 



same in an atmosphere containing 8 per cent, of oxygen as in one 

 containing a much larger proportion of this gas or in a pure oxygen 

 atmosphere. 



A low concentration of oxygen beyond which no growth of 

 cells will take place was also recorded. But as stated this was 

 not accurately determined. There were certain discrepencies in 

 the method of measurements and as must be stated here the 

 tissues used for determining this point were fragments of the 

 heart of 15, 16, and 18 day old chick-embryos. 



In the present experiments, these objections to the technic used 

 as outlined in the previous paper have been removed and tissues 

 from embryos of various ages have been tested. The tissues 

 chiefly used have been fragments of the heart muscle and body 

 wall of 4 and 5 day old, 10 day old, and 15 day old chick-embryos. 



One criticism of Fletcher's work is that he used a muscle of 

 considerable thickness and in which the gaseous exchange must 

 have been slow. I think, however, as Bayliss states, that this 

 objection was obviated by his second experiment where he placed 

 the fatigued muscle from the atmosphere of nitrogen into one of 

 oxygen and noted a recovery from the fatigue. 



I measured the distance oxygen diffuses readily into clots of 

 blood, clots of plasma, and into tissue by means of the color changes 

 in red cells. Into clots of chicken's blood the diffusion takes place 

 readily only into a surface layer of 0.5 to 0.7 mm. in thickness. 

 The hemoglobin in red cells lying below this layer or which are 

 separated from the air by a layer of clotted plasma of that thick- 

 ness becomes readily and permanently reduced. In this surface 

 layer they maintain a bright red color. 



In tissues the diffusion of oxygen may be more. It may exceed 

 3 mm. There are variations, however. 



In all of these experiments fragments of tissue less than a mm. 

 in diameter were used. They were planted in a layer of plasma 

 0.5 mm. or less in thickness. The culture chambers were made 

 from one piece of glass tubing prepared according to the manner 

 described in the previous papers (loc. cit.). The gas to be tested 

 was passed through the chamber intermittently for from 1 to 2 

 hours. The capillary tube inlet and outlet were then sealed in 

 the flame. 



