AND ITS EFFECTS UPON ANIMAL LIFE. 25 



any iieculiar volatile poisonous matter in the air expii-ed by healthy men and 

 animals, other than carbonic acid. Tt must be borne in mind, however, that the 

 results of such experiments upon animals as are referred to in tliis i-epoi-t may be 

 applicable only in part to human beings. It does not necessarily follow that a 

 man would not be injured by continually living in an atmosphere containing 2 

 parts per 1000 of carbonic acid and other products of resi)ii-ation, of cutaneous 

 excretion, and of putrefactive decomposition of organic; matters, because it is found 

 that a mouse, a guinea-pig, or a rabbit, seems to suffer no ill effects from living 

 undei- such conditions for sevei'al days, weeks, or months, but it does follow that 

 the evidence which has heretofore been supposed to demonstrate the evil effects of 

 bad ventilation upon human health should be carefully scrutinized. 



VI. The effects of reduction of oxygen and increase of carbonic acid to a 

 certain degree appear to be the same in artificial mixtures of these gases as in air in 

 which the change of proi)ortion of these gases has been produced by respiration. 



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

 phere 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 fi-esh air 

 into it dies almost immediately, has been observed befoi-e, but we are not aware 

 that a continuance of this immunity produced by it had been previously noted. 

 The experiments reported in the Appendix, VII., 17 to 28, show that such an 

 immunity may either exist normally or be produced in certain mice, but tliat these 

 cases are very exceptional, and it is veiy 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 respiratory centres 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 

 becomes more urgent. 



So far as the acute effects of excessively foul air at high temperatures are 

 concerned, such, for example, as appeai'ed in the Black Hole at Calcutta, it is 

 probable that they are due to substantially the same causes in man as in animals. 



IX. The proportion of increase of carbonic acid and of diminution of oxygen, 

 which has been found to exist in badly ventilated churches, schools, theatres, or 

 barracks, is not sufficiently great to satisfactoi'ily 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 



