1856.] and the Means of Determining its Amount 241 



poisonous than carbonic acid, but we do not know that this is a 

 fact. The best example I can give you of an animal substance in 

 a stale of decomposition is musk, and yet it is no highly poisonous 

 substance ; but even if these animal substances are not poisonous, 

 still, as the offensiveness perceived by a person just entering from 

 the fresh air bears an inverse proportion to the dilution of the air 

 in the room by fresh air, the offensiveness to such a person may be 

 taken as one test of the want of ventilation. 



Another part of the physiological method consists in determi- 

 ning the general action of the air of the room on the body inside as 

 well as outside, on the nerves, muscles, skin, and mucous mem- 

 branes. 



Carbonic acid, in very large doses, immediately destroys life by 

 stopping the breath, but of this rapid action there is no question. 

 What we want to know is, — What is the action of the smallest 

 injurious doses? Carbonic acid, like other poisons in small doses, 

 is a medicine. We take it in soda water, and in effervescing medi- 

 cines to allay irritation. It is used as a douche ; at first exciting 

 the eyes or the nose, and soon allaying irritation. 



Like other medicines its effects vary with the age of the person 

 taking it, with the time during which it is continued, with the 

 strength of the dose, and with the peculiarities of the individual. 

 A very small dose, long continued, will produce effects, whilst the 

 same dose, in a short time, may give no perceptible result. The 

 action of a full overdose may be well compared with the action of 

 sether, of an overdose of alcohol, or of chloroform. At first 

 irritation, then slight giddiness, intense giddiness, desire to vomit, 

 excessive prostration, inability to make any muscular effort, syncope, 

 death. 



The symptoms from small doses, long continued, closely resemble 

 the symptoms from smaller doses of alcohol, long continued ; slowly 

 the nutrition of the textures of the body is affected ; debility, 

 unhealthy blood, passive congestions, low inflammations, especially 

 of the mucous membranes, and broken skin, with ulceration and 

 gangrene, are produced. 



If these effects are observed in any atmosphere, then the venti- 

 lation is proved to be insufficient. 



2. The physical method consists in determining the velocity of 

 the air passing out of the room or into the room, either by calcula- 

 tion or by experiment. 



The mean temperature of the air in the chimney is determined. 

 Hence the increase in volume of the air is known. This volume of 

 heated air is then compared with the volume of an equal weight 

 of cold air. The difference in height in these two volumes of air 

 is obtained, and the force of the draught is equal to the velocity 

 which a heavy body would acquire by falling freely through this 

 height. The velocity of a falling body, in feet per second, is equal 



r2 



