83 G. F. DOWDESWELL. 



sugar and salt solution required to produce contraction of the 

 filaments agrees witli De Vries' results. He remarks^ that about 

 25 per cent, of sugar solution is required to produce the same 

 amount of shrinking as is caused by 4 per cent, solution of 

 chlorides of sodium or potassium. 



If we compare the effects of dilute acetic acid and of salt 

 solution on the wall-protoplasm of the glands we find that both 

 cause shrinking, but that the results of the two reagents are 

 clearly distinguishable by subsequently irrigating with water. If 

 salt solution has caused the shrinking the cells rapidly recover, 

 but the shrinking caused by a poison is permanent. In the case 

 of the cell-protoplasm we clearly distinguish therefore between 

 the action of a ])oison and the mechanical withdrawal of water. 

 But in the case of the filaments precisely the same difi'erence is 

 found to exist between the action of salt solution and acid — 

 when tested by subsequent irrigation with water. ^ Therefore 

 the effects of salt solution being certainly mechanical, the eff'ect 

 of the acid seems to be probably poisonous, using poisoning to 

 mean 'a specific injurious action on living matter. 



Note on Atmospheric Bacteria. By G. F. Dowdeswell, B.A. 



Cantab. 



It has been observed both by Dr. Burdon Sanderson, in this 

 country, and by Prof. F. Cohn, in Breslau, that when atmo- 

 spheric air is drawn through a nutrient fluid in wash bottles, no 

 Bacteria are developed. To elucidate the cause of this, a series of 

 experiments has been made, in which the method adopted was 

 to put about 100 c. c. of Cohn^s normal cultivating solution^ in 

 each of several wide-mouthed bottles, previously superheated, 

 then boiling the solutions, covering the bottles with watch glasses, 

 and placing them in the incubator at 35° C. for some days, to 

 ascertain if they were free from organisms, as tested by their 

 contents remaining pellucid ; they were then fitted with caout- 

 chouc stoppers, through which glass tubes were inserted, to draw 

 air through the solution, each tube being bent once at a right 

 angle, excepting the egress tube of the last bottle, which was 

 straight, plugged with cotton wool at both ends, and connected 



' Loc. cit., p. 11. 



' It not only cannot recover its normal extended condition, but swells up 

 and forms a " soap-bubble " mass which can be made to contract and swell 

 out again by alternations of salt solution and water. Tiiis eilect, which is, 

 of course, mechanical, is cpiite different from the extension and contraction 

 of a fdament wiiicli has not been treated (killed) with acid, quinine, &c. 



» Pot. Phosp., 1-0, Mag. Sulph., I'O, Ca. CI., 0-1, Amm. Tart., 2-0, and 

 Aq., 200. 



