130 RESPIRATION 



pressures and tensions until the pressure is lowered to yV f 

 an atmosphere. From y^ to -fa f an atmosphere the great 

 bulk of 62 is given off. Below -fa, physical laws, as given 

 above, again prevail. The explanation of this is that the O2 

 is held in chemical combination with the hemoglobin, and is 

 set free at T V to -fa f an atmosphere. This pressure is termed 

 the tension of dissociation. 



Venous blood contains 45 volumes of CO 2 in 100. Of this, 

 5 per cent, is in simple solution, 10 to 20 per cent, in firm 

 chemical combination, and 75 to 80 per cent, in loose chemical 

 combination. The largest amount is connected with the 

 red blood cells. While the CO2 absorbed by water increases 

 regularly with the increase of pressure, that absorbed by solu- 

 tions of hemoglobin is relatively large for low pressures and 

 small for high pressures. The quantity in the blood is in excess 

 of what physical laws will permit. It is found that the partial 

 pressures of 62 and CO2 in venous blood are about 22 and 41 

 mm. Hg respectively. Comparing the pressures of 62 in the 

 lung, alveoli, blood, and tissues (152, 100, 22, 0) with those 

 of CO 2 (0.3, 35, 41, 58), it is seen that O 2 and CO 2 will diffuse 

 in opposite directions. Pure oxygen at a pressure of 1 atmos- 

 phere may be breathed without injury. At higher pressures 

 it acts as an irritant and produces inflammation. When less 

 than 10 volumes of oxygen are present in the air in 100, it is 

 insufficient to maintain the life of man. Pure 62 is fatal in 

 from two to three minutes. N, H, and CH 4 cause no incon- 

 venience if sufficient 0% is present. Nitrous oxide and ozone 

 produce anesthesia, and finally death. Air containing 20 

 volumes of CO2 in 100 is rapidly fatal. 



Eupnea is normal, easy breathing. Apnea is a condition 

 of suspended breathing. Hyperpnea is increased respiratory 

 activity. Polypnea is a condition of deep, labored breathing. 

 Asphyxia is characterized by convulsive breathing, followed 

 finally by infrequent and feeble respirations. Apnea can be 

 induced in man or animals by rapid, deep respiratory move- 

 ments or by forcing air into the lungs with a bellows. It is 

 brought about by using pure 62 or H 2 ; lasting for a longer 

 time when the former is used. But the fact that it can be 

 produced with H 2 shows that the condition cannot be due to 

 a superabundance of 62 in the blood. It is believed that in 



