THE EXTERNAL ENVIRONMENT 251 



ness. The workmen enter the diving bell after the compressed 

 air has gradually driven out the water. The pressure depends 

 on the depth at which they have to work. It is 1 atmosphere 

 per 10-33 m. But work is rarely carried out under a pressure of 

 more than 5 atmospheres. 



In these circumstances, the breathing becomes slower, and, 

 consequently there is less intensity of interorganic combustion. 

 The blood dissolves a greater quantity of gas, that is to say, of 

 nitrogen and oxygen. Thus we find, in the blood : 



OXYGEN NITROGEN 



At normal pressure 20% 2-2% 



At 6 atmospheres 23% 6-5% 



In other words, there is an excess of 30 cubic centimetres of 

 oxygen and of 43 cubic centimetres of nitrogen per litre of cir- 

 culating blood. For an adult, the blood represents a total volume 

 of about 4,500 cubic centimetres, of which 135 and 194 cubic 

 centimetres of gas tend, at the moment of decompression, to leave 

 the blood and to be evolved in the cellular tissue. This causes 

 pricks, itching and sometimes tumefaction in the workmen. The 

 moment of decompression is certainly the most to be feared. 



These gaseous embolisms can be fatal ; they are more serious 

 and more frequent in fat persons. The constituent element is 

 nitrogen, because the oxygen remains fixed in the tissues. Hill 

 even recommended inhalations of oxygen to facilitate the de- 

 parture of the nitrogen without serious danger, f 1 ) Other acci- 

 dents, not really very serious, also occur in diving ; there is a 

 singing in the ears, sometimes painful, but which the workmen 

 get rid of by a swallowing movement. Other facts which belong 

 to industrial hygiene cannot be mentioned ; it is enough to point 

 out the diminution of the phenomenon of oxydation (the sole 

 source of energy) which must result in a decrease of dynamic 

 capacity. This decrease has not been exactly estimated. Men 

 who work in compressed air complain also of a certain rigidity 

 in the joints which impedes their movements. 



184. Influence of Deleterious Gases and Vapours. The atmos- 

 phere, whose theoretical composition has been previously given 

 ( 164), and which was then considered to be in a state of purity, 

 is, as a matter of fact, never pure in a place where men are gathered 

 working. Carbonic acid gas and carbon-monoxide are the most 

 frequent causes of vitiation ; the former is only dangerous in 

 large quantities ; but the latter, which has the property of fixing 

 itself energetically on the hcemoglobin of the blood, is a formid- 

 able poison, even in the proportion of 0-2 to 0-3% of the atmos- 



( x ) Revue Gin des Sciences, 1910, p. 954. See an article by Hill in the 

 British Medical Journal of 17th Feb., 1912. 



