70 J, S. MC'iNTIRE ON CHEAP AIDS TO MICROSCOPICAL STUDIES, 



Fitzgerald, the associate of Mr. Whitney in his researches on 

 that interesting creature, to bring it under the notice of the club. 

 Two pieces of stout brass, about five inches by two inches, hav- 

 ing large central perforations, over which thin glass is placed, are 

 kept apart by a very stout India-rubber ring and bound together 

 at the ends by screws, which are entirely removable. Few pieces 

 of optical apparatus are so simple, and no animalculae cage or 

 compressorium that I know of answers the particular purpose 

 for which this was made so perfectly. Not many observers are 

 aware of the wonderful sight that the interior economy of the 

 tadpole of the frog affords for a few days during its life ; per- 

 haj)s three days, four at most. At this period the skin of the 

 belly is nearly transparent, and the blood in the internal gills 

 and heart has become conspicuously brilliant — I suppose from its 

 increased quantity. But I will not venture to describe the sight, 

 as I fear I should soon get out of my depth in the attempt to 

 deal with a subject so purely physiological. It is, nevertheless, 

 most interesting and wonderful, as affording more than a glimpse 

 of some of the mysterious operations going on in the very seat 

 of life. To use the apparatus the two pieces of brass are 

 separated, enabling the tadpole and a spoonful of water to be 

 introduced into the cell formed by the India-rubber ring, which 

 must be of proper thickness. Then the top piece of brass is put 

 in its place, and the ends are screwed tightly together. The ends 

 of the screws should permit either side of the apparatus to be up- 

 permost on the stage of the microscope. The tadpole must be 

 examined belly upwards, a position it cannot endure, so it makes 

 violent efforts to right itself, and if the ring be too thick it will 

 succeed, and turn over ; on the other hand, if it be too thin the 

 tadpole may be crushed by the pressure. Thus, rings of varying 

 thickness are necessary. The inch and half power is the best for 

 examination, and some means of condensing the light from the 

 mirror must be adopted. The best effects I have seen were with 

 Smith and Beck's 1^ objective and Powell's condenser, from which 

 the front lenses had been removed.* 



I feel strongly tempted to speak of Mr. Curties's new growing 

 slides, having for a long time past had a partiality for the cells 

 he has improved upon by the addition of a sliding cover, but 



* A common spot lens, with adjustable spot, answers admirably for similar 

 purposes. — Ed. 



