156 Scientific Intelligence. 



mixtures of these gases as in air in which the change of propor- 

 tion of these gases has been produced by respiration. 



VII. The effect of habit, which may enable an animal to live 

 in an atmosphere in which, by gradual change, the proportion of 

 oxygen has become so low, and that of the carbonic acid so high, 

 that a similar animal brought from fresh air into it dies almost 

 immediately, has been observed before, but we are not aware that 

 a continuance of this immunity produced by it had been previ- 

 ously noted. The experiments reported in the Appendix, VII, 

 \1 to 28, show that such an immunity may either exist normally 

 or be produced in certain mice, but that these cases are very 

 exceptional, and it is very desirable that a special research should 

 be made to determine, if possible, the conditions upon which such 

 a continuance of immunity depends. 



VIII. An excessively high or low temperature has a decided 

 effect upon the production of asphyxia by diminution of oxygen 

 and increase of carbonic acid. At high temperatures the respir- 

 atory centers are affected, where evaporation from the skin and 

 mucous surfaces is checked by the air being saturated with 

 moisture ; at low temperatures the consumption of oxygen 

 increases, and the demand for it becames more urgent. 



So far as the acute effects of excessively foul air at high tem- 

 peratures are concerned, such, for example, as appeared in the 

 Black Hole at Calcutta, it is probable that they are due to sub- 

 stantially the same causes in man as in animals. 



IX. The proportion of increase of carbonic acid and of dimi- 

 nution of oxygen, which has been found to exist in badly venti- 

 lated churches, schools, theatres or barracks, is not sufficiently 

 great to satisfactorily account for the. great discomfort which 

 such conditions produce in many persons, and there is no evidence 

 to show that such an amount of change in the normal proportion 

 of these gases has any influence upon the increase of disease and 

 death-rates which statistical evidence has shown to exist among 

 persons living in crowded and unventilated rooms. The report 

 of the commissioners appointed to inquire into the regulations 

 affecting the sanitary conditions of the British army (1), prop- 

 erly lays great stress on the fact that in civilians at soldiers' ages, 

 in twenty-four large towns, the death-rate per 1000 was 11.9, 

 while in the foot-guards it was 20.4, and in the infantry of the 

 line 1*7.9, and showed that this difference was mainly due to dis- 

 eases of the lungs occurring in soldiers in crowded and unventi- 

 lated barracks. These observations have since been repeatedly 

 confirmed by statistics derived from other armies, from prisons, 

 and from the death-rates of persons engaged in different occupa- 

 tions; and, in all cases, tubercular disease of the lungs and pneu- 

 monia are the diseases which are most prevalent among persons 

 living and working in unventilated rooms, unless such persons are 

 of the Jewish race. But consumption and pneumonia are caused 

 by specific bacteria, which, for the most part, gain access to the 

 air-passages by adhering to particles of dust which are inhaled > 



