EFFECTS OF VITIATED AIR 317 



slowing of the heart by stimulation of the vagus center from lack of 

 oxygen. 



It must be kept clearly in mind that the respiratory changes just 

 described as characteristic of asphyxiation are the secondary results of the 

 primary general tissue asphyxiation. If an animal is deprived of its income 

 of oxygen, and its ability to eliminate the product of oxidation, carbon 

 dioxide, the nutritive balance around the peripheral tissues is immediately 

 disturbed. The result is that tissue metabolism such as occurs is deranged. 

 If oxidations are incomplete, intermediary products accumulate and on 

 the whole the physiological life of the tissue is rapidly blocked. The 

 average organ of the human body can endure only a certain degree of as- 

 phyxiation before changes occur which destroy, in whole or in part, the 

 protoplasmic organization. Of all the tissues the nervous tissues are most 

 susceptible to asphyxiation. The generalized tissues, the epidermis, con- 

 nective tissue, etc., are most resistant. Life is jeopardized by injury to the 

 weakest point, hence the body as a whole will not recover from complete 

 asphyxiation which endures for a time greater than that which the nervous 

 tissues will withstand. Stewart, Guthrie, Burns and Pike have set the 

 limits very low for this tissue, from 7 to 16.5 minutes. However, incomplete 

 asphyxiation is a condition difficult to determine, and the less complete the 

 asphyxiation, the greater the probability of recovering the normal tissue 

 activity. In all those conditions of life in which accidental asphyxiation 

 occurs, it must be assumed that we are dealing with one of partial asphyxia- 

 tion, especially in all efforts at resuscitation. 



Cheyne-Stokes' breathing is a rhythmical irregularity in respirations which 

 has been observed in various diseases. Respirations occur in groups. At 

 the beginning of each group the inspirations are very shallow, but each 

 successive breath is deeper than the preceding, until a climax is reached. 

 The inspirations then become less and less deep, until they cease altogether 

 for a time, after which the cycle is repeated. This phenomenon appears to be 

 due to the want of action of some of the usual cerebral influences which pass 

 to, and regulate the discharges of, the respiratory center. 



Effects of Vitiated Air. Ventilation. As the air expired from the 

 lungs contains a large proportion of carbon dioxide and a minute amount 

 of organic matter, it is obvious that if the same air be breathed again and 

 again, the proportion of carbon dioxide and organic matter in it will con- 

 stantly increase till it becomes unfit to breathe; long before this point is 

 reached, however, sensations of uneasiness occur, such as headache, languor, 

 and a sense of oppression. It is a remarkable fact, however, that the organ- 

 ism after a time adapts itself to a very vitiated atmosphere, and that a person 

 soon comes to breathe, without sensible inconvenience, an atmosphere which, 

 when he first enters it, feels intolerable. Such an adaptation, however, can 

 take place only at the expense of a depression of all the vital functions, which 



