186 



THE AMERICAN MONTHLY 



[October, 



in 80 per cent, alcohol, 6.9 micro- 

 millimetres (or :r^V?r inch.) 



Mosquito blood averages in di- 

 lute glycerin, 1.8 micro-milli- 

 metres (or TToTrir inch) ; in 80 per 

 cent, alcohol, 1.4 micro-millimetres 

 (or T^U^ inch.) 



The subject appears to me to be 

 of sufficient importance to deserve 

 further investigations. However 

 much we may regret that another 

 prop is taken from the value of cir- 

 cumstantial evidence, derived from 

 suspicious stains in murder cases, it 

 is best to know and make proper 

 allowance for any weak points of 

 such information. For even if 

 stains should now be fully identi- 

 fied as derived from human blood, 

 the accused may plead in his justi- 

 fication, that they are due to the 

 agency of insects, and cannot be 

 allowed to furnish any proof of his 

 guilt. 



Since reading the above paper 

 before the Society, investigations 

 on the bed-bug (as yet very few 

 in number) appear to show that the 

 imbibed human blood is destroyed 

 far more rapidly in them than in 

 the mosquito. In one individual, 

 after twelve hours, not a trace of 

 the human blood-corpuscle could 

 be detected. 



St. Louis, Mo. 



A Mechanical Finger. 



I have constructed for my micro- 

 scope mechanical fingers in two 

 ways which may be followed by 

 any one desiring such an ap]3liance 

 and having a stage forceps only, or 

 still better, a forceps and a nose- 

 piece also. 



(1) By taking a strip of pine wood 

 half an inch thick, and of suitable 

 length and breadth, and giving it a 

 suitable shape, making a hole in 

 the larger end of such size, that 

 when lined with a bit of cloth, it 



fitted tightly on and over the nose 

 of my one-inch objective. In the 

 smaller end was made another hole 

 into which a slightly tapering cork 

 was pressed from above, in order to 

 carry the forceps. Having fastened 

 a bristle into the jaw of my stage- 

 forceps, by means of a drop of glue, 

 and made a small hole for a guide, 

 the shank of the forceps was 

 forced into the cork and fastened in 

 position with sealing-wax, and the 

 finger was complete, with no ex- 

 pense but an hour's labor. 



(2) With still less labor, I substi- 

 tuted my nose-piece for the above 

 wooden carrier ; screwing the cork 

 into the nose-piece, instead of the 

 extra objective, and attaching the 

 forceps as before. 



In either case, the elasticity of 

 the cork holds it in place with suf- 

 ficient firmness to admit of its be- 

 ing rotated with finger and thumb, 

 so as to move the point of the forceps 

 with the bristle to the right or 

 left as may be desired. The lifting 

 of the object is done by means of the 

 joint in the forceps. 



Although the fingers here sug- 

 gested may not be as perfect as 

 those of a more costly and finished 

 construction, yet combining as they 

 do all movements essential to any 

 finger, they may be used in an 

 emergency, and in skilful hands 

 will be found capable of effective 



work. J. SULLIVANT. 



CoLuisEBUs, Ohio. 



On the Presence of the Forms 



of Life in the Central and 



Lateral Surface Waters 



of Lakes and Ponds. 



BY EPHBAIM CUTTER, M. D. 



I have seen it stated that over 500 

 municipalities and towns in this 

 country are supplied with hydrant 

 water. As a physician I have been, 

 mucli interested in studying the in- 



