ON THE CARBONIC ACID, ORGANIC MATTER, ETC., IN AIR. 
77 
class of house. Contrary to expectation, the mortality from diphtheria and croup 
does not show any connexion with the class of house.* 
(7.) It is seen that deaths certified as being due to “old age” do not run parallel 
with the different classes of houses, though one would have expected that they would 
have done so, and that the numbers would have diminished from 4- to 1-roomed 
houses. “ Old age” is a somewhat indefinite term as a cause of death, and would be 
materially affected by the mode in which the doctors filled in the certificates; so that 
it does not form a safe indication of the number of people of advanced age living in the 
various classes of houses. A reliable indication of this, however, is furnished by the 
death-rate of persons who die above 70 or above 80 years in the different classes of 
houses; and, as already remarked above, this shows a complete parallelism, and proves 
conclusively that there is a much larger proportion of old people living in the better 
than in the worse class of houses. 
The effects of impurity in air on the death-rates from different diseases are more 
particularly discussed below (page 105). 
The Air of Schools.! 
In the course of our investigations we have examined the following schools and 
other educational institutions in Dundee :— 
(a.) Sixteen ordinary Board schools (all the schools under the Dundee Board).— 
Two rooms were examined in each school. Some of the schools were heated by fires 
and others by hot pipes. They were all ventilated by the ordinary means usually 
adopted in such buildings, viz., fires, ventilators in the roof, and open windows. The 
great majority of the latter opened by means of hinged panes, opening obliquely so as 
to direct the entering current upwards. 
(b.) The Harris Academy. —This school is also under the Board, but is of a higher 
grade than the ordinary Board schools, and the children are of a higher class. 
Fifteen rooms were examined in this school on various occasions and under different 
conditions. Of those examined, twelve rooms were mechanically and three naturally 
ventilated. 
(c.) A half-time school belonging to one of the large mills in the town.—The two 
rooms (one for girls and the other for boys) were frequently examined under different 
conditions. The children in this school are employed half the day in the mill, and are 
at school the other half. This school was ventilated mechanically. 
(d.) Two denominational schools. —Two rooms in each ; these were naturally venti¬ 
lated and heated by fires. 
* Rorosi (loc. cit.) has shown that the mortality from infections diseases generally increases with the 
density of the population, and that this is most marked in the case of hooping-cough and measles, but is 
not evident with scarlet fever and diphtheria. (Cf. below, p. 107.) 
t See also Supplementary Note, p. 111. 
