226 THE AMERICAN MONTHLY [Dec 



object-g-lass, an oi'dinary thin g-lass cover may be placed 

 over it to keep the tail steady. The tadpole can be kept 

 thus for an hour or more withoutany apparent discomfort, 

 provided that the cotton-wool be kept moist. It mig-ht be 

 mentioned that the tadpoles are of very little use for this 

 object after the development of the leg's, as the circulation 

 then ceases, and the tail becomes opaque. I always use a 

 one-inch objective and dark g-round a illumination. — Lewis 

 H. T. Chase in Science Gossip. 



Photo-micrography with High Powers, — In "Nature" 

 Messrs. J. E. Barnard and T. A. B. Carver explain how 

 they have overcome the difficulty experienced in photo-mi- 

 crog-raphy with hig-h powers and critical illumination, 

 owing- to the unequal intensity of the lig^ht emitted from 

 the surface of incandescent limes, or the impossibility of 

 controlling- the electric arc so as to maintain a constant 

 position and condition of the crater on the positive carbon. 

 The latter difficulty has now been overcome by having- a 

 simple form of hand-feed apparatus, with a pinhole camera 

 attached, throug-h which an imag-e of the carbon points is 

 projected onto a g-round-glass screen. With such a form 

 of arc-lamp absolute "centration" of the lig-ht can be se- 

 cured and mantained, without reference to the microscope, 

 after the necessary position of the image of the arc on the 

 screen of the pin-hole camera has been once obtained. 



Effect of Different Media on Micro-organisms. — Profes- 

 sor Bitting has found by making ten exposures each of 

 air, water and milk upon four different media (neutral 

 ag-ar ag-ar, neutral g-lycerine ag-ar, neutral beef g-elatine 

 and slig-htly acid wort g"elatine) using- some closed petri 

 dishes all under like conditions, that ag-ar ag-ar g-ave 

 the most bacteria and wort g-elatine the most moulds. 

 The averag-e number of colonies of bacteria devel- 

 oped by ten tests of air was : On ag-ar ag-ar, 86 ; g-ly- 

 cerine. 73 ; beef g-elatine, 64 ; wort g-elatine, 41. Ten tests 

 of water g-ave the following- number of colonies : Ag-ar- 

 ag-ar, 2,370; g-lyceiine ag-ar, 2,260; beef gelatine, 1,470 ; 

 wort g-elatine, 480. Ten tests of milk g-ave the following- 



