460 REPORTS ON THE STATE OF SCIENCE. 



per hour must be supplied to each inmate for that purpose. There would 

 he no advantage from the point of view of freshness in having it merely 

 cooled by walls or windows ; and hence, without laying too much stress on 

 the precision of the numeral calculations, a supply less than 2,000 must 

 be regarded as inadequate. 



A third consideration is the removal of the solid and liquid particles 

 which find their way into the air from the skin or clothing, or from the 

 mouth, or by raising the dust from the floor and surfaces of seats, desks, &c. 

 These particles, which often carry organisms, pathogenic or otherwise, 

 may be regarded from the physical point of view as fine dust which is 

 constantly in process of settling, but so slowly that the greater part of it 

 takes part even in the slow circulation of the air in an inhabited room. 

 It can hardly be denied that these particles when associated with or 

 derived from infectious sources may form the most injurious constituents 

 of a vitiated atmosphere. We know little of their size or nature, but 

 their behaviour in the air must be represented more or less aptly by that 

 of the cloud of particles which constitutes tobacco smoke, and we may 

 judge from the behaviour of such a cloud what is the best course to pursue 

 in order to remove the obnoxious particles. On this analogy it is clear 

 that the less vigorous the circulation of air through the room the more 

 the particles hang about the room, and we have thus another reason for 

 maintaining the flow of air at the highest figure compatible with the comfort 

 of the occupants. 



Von Pettenkofer's method of estimating the quantity of air required 

 by considering the dilution of carbonic acid draws a distinction between 

 adults and children, The considerations which have been adduced tend 

 to show that the introduction of any such distinction in practical ventila- 

 tion would indicate a degree of accuracy in our knowledge of the pro- 

 cesses of ventilation to which we can lay no claim. Even if it be true 

 that the production of carbonic acid increases with the body weight, it is 

 not a necessary consequence that the natural demand for fresh air increases 

 in the same proportion, and we are not prepared to say that a boy or girl 

 should be supplied with less air than a man or woman. 



"We may sum the considerations by saying that a supply of 1,000 cubic 

 feet per head per hour to healthy occupants will barely save the room 

 from becoming disagreeable. A supply of 2,000 cubic feet is the smallest 

 that can be recommended for health, mental energy, and comfort. More 

 still would be required in order to approach the conditions of ideal venti- 

 lation. 



The Suitable Degree of Temperature and Humidity. 



Recent investigations, more especially those of Haldane and others in 

 this country, of Fliigge and Paul in Germany, have shown that the 

 temperature of a room and of the air supplied is of greater importance 

 than has generally been supposed ; that a high degree of temperature in a 

 room {e.g., above 68° F.) produces languor, sense of mental fatigue, and the 

 other symptoms associated with crowded assemblies, to a greater extent 

 even than polluted air ; and that these symptoms are aggravated by stag- 

 nation and immediately relieved by movement of the air surrounding the 

 body. 



These results have been confirmed by the careful observations sug- 

 gested by the work of this Committee and recently carried out in the 

 London schools. 



