98 PROF. T. CARNELLEY, MR. J. S. HALDANE, AND DR, A. M. ANDERSON 
Although the condition as regards ventilation during short periods of time may be 
of slight influence on the organisms in air, yet the habitual condition seems to exercise 
a marked influence. 
In the mechanically ventilated half-time school, just referred to, the average of all 
the observations made diming occupation (including those with the ventilation off) 
was 34 per litre. The school is a very old one, and the scholars come straight from 
the mill to the school in their work clothes. The air in the spinning flat of the mill 
itself had been found to contain about 600 micro-organisms per litre. All the con¬ 
ditions except the habitual ventilation are thus in favour of a very high number of 
micro-organisms. Nevertheless, the number found is less than a fourth of the average 
number found in naturally ventilated Board schools (155), a sixth of that in the 
dirtier naturally ventilated schools, and a ninth of that in the older naturally 
ventilated schools. 
Unfortunately, the rooms in the Harris Academy provided with mechanical venti¬ 
lation are very much newer than those without it, so that the two sets of rooms are 
not strictly comparable. But, from the exceedingly low results in the High School 
(an old school), it is probable that age makes very little difference with mechanical 
ventilation. The average in the mechanically ventilated rooms of the Harris Academy 
was 16 per litre, whilst in the naturally ventilated rooms of the same school it was 117. 
Even if we make a large allowance for difference in age, the contrast is still very 
striking. The number is more than thrice as great as in the mechanically ventilated 
half-time school referred to above, in spite of the age of the latter, and of the 
scholars being much less clean. 
Lastly, we may compare the naturally ventilated private school referred to previously 
against the High School. The cubic space and age were about the same. The 
private school was exceedingly clean and quiet, and there were no boys in it. Every 
condition was in its favour, except that the ventilation was by natural means. The 
average in the private school was 9'3 ; that in the High School 3‘6. Both numbers 
are, of course, low. 
D. In order to show the influence, if any, of age (probably as conditioned by 
cleanliness), we have classified the naturally ventilated Board schools as follows;—- 
No. of cases. 
Micro-organisms 
per litre. 
Opened before 1866 .... 
7 
311 
„ 1875-1880 .... 
20 
150 
„ 1884-1885 .... 
5 
38 
Unfortunately, in the case of the oldest division of schools, in all but one case the 
children were exceptionally dirty, so that nothing can fairly be deduced from the 
number for this class. 
