2i2 THE MICROSCOPE. 



o 



A Substitute for a Revolving Table. — Board set on 

 rollers and carrying the microscope and lamp round a house table 

 by revolving on a centre through the medium of an arm on stalk. 

 As a screw put into a mahogany table would be objectionable, a 

 centre is made of two disks of wood between which the stalk re- 

 volves freely on a screw, a 10 lb. weight on the uppermost disk pre- 

 venting the centre from slipping about the table. 



The Microscopic Examination of Water. — The Rep. 

 Anal. Chemic. states that J. Brautlecht produces a precipitate in the 

 water by adding to one hundred c. c. five drops of a solution con- 

 sisting of one part aluminum sulphate, one part hydrochloric acid, 

 and eight parts water, followed up by one to three drops of liquid 

 ammonia. t The precipitate settles readily, and after decanting off 

 the clear liquid, is collected upon a smooth filter, stroked off with a 

 glass rod, and thus transferred to a. test tube, in which it is dissolved 

 in ten to fifteen drops of dilute acetic acid. The clear solution is 

 examined with the microscope, at first alone, and, then after the ad- 

 dition of a solution of saffranine. By adding j4 per cent, of gelatin, 

 permanent preparations may be obtained on Koch's principle. 



The Mutability of Bacteria. — The question whether the 

 same germs under different conditions give rise to various diseases 

 has been raised, but not settled. Dr. Carpenter, at the meeting of 

 the British Association, treated the subject from a point of view of 

 natural history. He referred to the facility which the lower forms 

 of life possess of adapting themselves to changed conditions of ex- 

 istence. He believes that the same germs may, under altered cir- 

 cumstances, produce various diseases, and these opinions he sup- 

 ported by various arguments. The decrease of the virulence of the 

 small-pox which ravaged Europe in the fifteenth century he attri- 

 buted to the cultivation of the mildest cases which occurred. A 

 severe attack of any particular disease may so affect the system that 

 a disease arises which canhot'be recognized as related to that from 

 which it proceeded. Under favorable conditions an ordinary inter- 

 mittent fever may develop into a virulent form, which is highly con- 

 tagious. There is, in his opinion, very strong ground for the belief 

 that even the innocent hay bacillus may undergo such an alteration 

 in its type as to become the germ of severe disease. 



