SCHOOL-ROOM VENTILATION. 531 



My interpretation of the matter, to a certain extent, is this : That the 

 visionary tendency is much more common among sane people than is 

 generally suspected. In early life, it seems to be a hard lesson to an 

 imaginative child to distinguish between the real and visionary world. 

 If the fantasies are habitually laughed at, the power of distinguishing 

 them becomes at length learned ; any incongruity or nonconformity is 

 noted, the vision is found out and discredited, and is no further at- 

 tended to. In this way the tendency to see them is blunted by repres- 

 sion. Therefore, when popular opinion is of a matter-of-fact kind, the 

 seers of visions keep quiet ; they do not like to be thought fanciful 

 or mad, and they hide their experiences, which only come to light 

 through inquiries such as these that I have been making. But let the 

 tide of opinion change and grow favorable to supernaturalism, then 

 the seers of visions come to the front. It is not that a faculty previ- 

 ously non-existent has been suddenly evoked, but one that had been 

 long smothered is suddenly allowed expression and to develop, with- 

 out safeguards, under the free exercise of it. Fortnightly Heview. 



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SCHOOL-EOOM YENTILATIOK 



Br P. J. HIGGINS, M. D. 



VENTILATION" is the supply of fresh air to an apartment, and 

 the removal of impure or vitiated air therefrom. An adequate 

 supply of free oxygen is absolutely necessary to animal life ; and, the 

 higher we ascend in the scale of that life, the greater the quantity of 

 oxygen consumed, and the more urgent the necessity for its consump- 

 tion. In the atmosphere this oxygen exists in a free state in mechani- 

 cal solution and in the form and proportion in which it is most easily 

 assimilable. From the atmosphere, the animal absorbs it by means of 

 its breathing apparatus which provides for its absorption by the blood, 

 and the blood carries it to the tissues. Pure air consists of a mechani- 

 cal mixture of about four fifths nitrogen and one fifth oxygen, with 

 traces of ammonia, and about one part in two thousand of carbonic-acid 

 gas (CO J. These latter (ammonia and COJ, from their small amount, 

 may be neglected. 



Air becomes vitiated for breathing purposes by holding in solution 

 other gases or substances whose presence interferes with the appropria- 

 tion of oxygen by the animal, or, being themselves absorbed, exert a 

 toxic influence upon the vital fluid and tissues of the body. Hence to 

 secure an adequate supply of fresh air, and the removal of impurities 

 that accumulate therein, are the objects of ventilation. In this paper 

 school-room ventilation only will be considered. 



A full-grown person breathes on an average about twenty times 



