ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 553 



tlie gas to escape, while in the latter case it escapes by itself lifting 

 up from time to time the cover-glass. 



As all objects or particles contained in the air or gas must be 

 at rest when examined with the higher power objectives, it will be 

 necessary to coat either the bottom of the cell, the cover-glass, or 

 both, with something to which the material will adhere as the gas 

 passes through. One of the best methods is to coat both the bottom 

 of the cell and under side of the cover-glass with a thin layer of 

 glycerine — somewhat after Beale's method of collecting aerial germs. 

 This coating is easily accomplished by previously moistening the 

 glass with alcohol. The rubber bag and connecting-tube may be 

 cleansed by drawing alcohol into them, and after expelling this they 

 may be easily dried, if desired, by drawing and expelling air for 

 awhile. 



All the parts being in proper connection, by opening the stop- 

 cock of the receiver, and gently pressing upon it, the cell may be 

 supplied at will. As before stated, any gaseous material can be 

 collected and kept any length of time from the access of air, and 

 when desired, directly examined under the Microscope without any 

 intermediate manipulation; "a great desideratum and one which 

 cannot be attained so far as I have been able to learn, by any other 

 slide or apparatus hitherto in use. Those most used are the 

 ■ Strieker ' and ' Hunt ' gas slides, the Holman ' life slide,' and the 

 animalcule cell or cage, none of which is applicable in examinations 

 with the higher power objectives ; and none of which, excepting one, 

 is arranged so as to allow of the direct introduction in small quantity 

 of gaseous material. The advisability, nay, the necessity, of more 

 perfect means for the examination of aerial or gaseous matter, must 

 have been felt by every one who has ever attempted any work in this 

 direction : and it is obviously only by patient investigation with hi»h- 

 power objectives that we can hope to discover the nature and habitat of 

 those infinitesimal organic poisons which are supposed to originate 

 in some unknown way the so-called zymotic diseases." 



Hardy's Compressorium.* — Mr. J. D. Hardy's object in con- 

 structing the compressorium shown in Fig. 98, is to remedy, to some 

 extent, the defects of existing compressors as regards the difficulty 



of regulating the pressure with exactness, the imperfect parallelism, 

 and a deficiency of freedom of action, which causes great risk of 

 losing or damaging the object under observation. 



* Journ. Quek. Micr. Club, i. (1882) pp. 35-6 (2 figs.). 



