82 BOTANICAL GAZETTE. 



possibly this difference of humidity might not be owing solely to the 

 presence of plants, the conditions were varied, and further observa- 

 tions made, with similar results. The manner in which these investi- 

 gations were carried out cannot be htre detailed. The following con- 

 clusion should, however, be quoted : "During the summer months, 

 when the windows are thrown widely open and the doors kept ajar, 

 the influence of transpiration is quite inconsiderable ; on the other 

 hand, when the interchange of air is not too rapid, a sufficient num- 

 ber of plants, well watered, have the effect (if the air be not 

 already saturated) of increasing the amount of moisture to a consider- 

 able extent." This point, as will be presently seen, is of special 

 importance where houses are heated by dry air furnaces." 



Then follows the record of a number of cases, from which the 

 following conclusions are drawn : 



"From the above cases it will be seen that what we Iiad deduced 

 from experimental results concernmg the health giving effects of 

 plants (which is owing to transpiration increasing the humidity of the 

 air, — -the plants acting as natural and perfect "atomizers") is entirely 

 in harmony with what is observed concerning the effect of sufficiently 

 moist warm air in many cases of phthisis, and if it is true, as we 

 have attempted to demonstrate, that house-plant hygiene constitutes 

 a valuable preventative measure where there is hereditary tendency 

 to certain diseases, then it ought to be definitely and thoroughly un- 

 derstood, and it is of vital importance that it should be adopted 

 in cases where there is known predisposition to phthisis, for half of 

 the cases are supposed to be preventable, whereas if the disease be 

 allowed to develop, complete recovery is not to be expected. Fur- 

 thermore, though the keeping of plants does not "cure" confirmed 

 cases of phthisis, it is nevertheless very useful to prolong life, and by 

 ameliorating the distressing symptoms renders existence at least en- 

 durable — an office not to be despised in such a wide-spread and ling- 

 ering disease. 



Observation teaches that advanced cases of phthisis (as, for in- 

 stance, where cavities exist) are benefitted by a more decidedly moist 

 atmosphere than is required in health, and hence they will require a 

 much greater profusion of plants in the room than those who have the 

 disease in a more incipient stage. 



The plants should be well selected and kept in a thriving condi- 

 tion. The chief points to be borne in mind in the selection of the 

 plants are, first, that they have soft, thin leaves ; secondly, foliage- 

 plants or those having extensive leaf-surface are to be preferred ; 

 thirdly, those which are highly scented (as the tuberose, etc.) should 

 be avoided, because they often give rise to headache and other un- 

 pleasant symptoms. 



In order to facilitate a practical application of the data gained by 

 experiment, the following formula has been carefully prepared : 

 Given a room twenty feet long, twelve feet wide, and ceiling twelve 

 feet high, warmed by dry air, a dozen thrifty plants with soft, thin 

 leaves and a leaf-surface of six square feet each would, if well 



