392 DISCOVERY REPORTS 



by being aerated. The volume of oxygen available in the other samples (one-fifth of the 

 volume of air supplied) would not serve materially to refresh the blood in its deoxygen- 

 ated state. The ratios recorded against these samples range from 2-io to 2-95 and their 

 average is 2-60. No nitrogen disappears when no oxygen is supplied (nos. io8c, d, logo), 

 the amount already in the blood being very small. This suggests that the main oxygen 

 consumption, apart from some small metabolic activity which the blood may possess, 

 is a factor in nitrogen disappearance. Control experiments showed no disappearance of 

 nitrogen in fresh pig's blood. 



If nitrogen is constantly being withdrawn from the blood by some mechanism such 

 as has been indicated above, it follows that on each successive dive there will be more 

 accommodation in the blood for nitrogen than would normally be the case, with the 

 result that but little nitrogen would be left in the lungs after a dive of some minutes' 

 duration ; but in actual fact the terrific blast of expiration shows without doubt that there 

 is plenty of nitrogen left in the lungs at the end of a longish dive. It is difficult to re- 

 concile these two facts with each other unless it be assumed that the circulation of a 

 whale is much slower than that of other mammals. In this connection it is perhaps 

 significant that the wall of the aorta of a Blue whale is remarkably thin, not more than 

 I cm. thick while the internal diameter is about 20 cm. If blood were being pumped at 

 high pressure the walls of the aorta might well be much thicker than this. Such blood 

 as does pass through the lungs will become supersaturated with nitrogen and will then 

 be cleared, but it seems unlikely that the whole of the whale's blood could course 

 through the lungs in the space of one dive. 



The application of the phenomenon of nitrogen removal to the prevention of caisson 

 sickness is obvious. The effect of slow circulation would be of course to diminish the 

 risk of caisson sickness, although not to abolish it altogether. Even if, as has been 

 suggested in the preceding paragraph, only a small portion of the blood becomes super- 

 saturated with nitrogen, that blood, in passing to certain organs, for instance the central 

 nervous system, will cause these in their turn to become supersaturated with nitrogen 

 which would become dangerous in the event of sudden decompression. 



MECHANISM OF NITROGEN REMOVAL 



Blood smears. Special samples of blood were taken from fresh whales and foetuses 

 for microscopic examination. These were drawn from arteries in the head, as mentioned 

 above, but with special precautions to ensure that all the apparatus used was sterile. 

 The collecting cannula and tube into which the blood flowed were wrapped in cloths 

 and steamed for 5 hours. The wrapping was removed at the instant of using, and the 

 tube was plugged with sterile cotton wool after being filled. 



Plain wet smears of this blood were examined microscopically with a 1/12 objective. 

 Apart from the usual formed elements of blood which were seen, such as erythrocytes, 

 leucocytes, etc., vast numbers of very small particles (hereinafter referred to as X 

 organisms) were seen in the plasma. Their shape was indefinite but approximately 



