490 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of its back stroke (L L', fig. 77). This wheel has about 120 teeth in its 
circumference. 
The wedge-slide is drawn backwards by a treadle T worked by the 
foot, acting through a cord which passes round a pulley P at one end of 
the trough. It is drawn forward by a cord and weight W attached to 
the opposite end of the wedge-slide and acting on a pulley P at the 
other end of the trough. The rate of movement of the slide is controlled 
partly by the amount of the weight attached to the cord, and partly by 
the foot hindering the rise of the treadle. The mechanism for raising 
the section is so arranged that the screw is rotated throughout the 
desired distance when the knife is at the end of its return journey 
and just in position to commence the cutting movement. When the 
wedge-slide is pulled backwards it strikes the upper end of a vertical 
lever arm L, which moves on a fulcrum fixed slightly below the side of 
the trough. 
The other end of the lever moves forward a horizontal rod L, which 
is attached to an arm A moving round the centre of the toothed wheel. 
This arm bears a ratchet which carries the wheel round through the 
desired distance. This distance again is regulated by the travel of the 
lever-arm, the wheel being the further carried round the greater the 
movement of the lever, and vice versa. The movements of the arm can 
be easily and finely adjusted by two small slotted bars O O f , attached by 
butterfly screws to the side of the trough. When the knife moves away 
from the lever, its lower end, and with it the rod and ratchet, are 
drawn back by a spring attached to the leg of the instrument. The 
ratchet is thus ready to move round the wheel when next the wedge- 
slide strikes the lever. The general arrangement of the mechanism is 
seen in fig. 77. 
The operator sits or stands at the side of the trough opposite to the 
groove in which the wedge-slide acts. He thus has both hands free 
for the manipulation of the sections. 
The instrument is made by Mr. Alexander Frazer, 22 Teviot Place, 
Edinburgh. It is already in use in my laboratory, Surgeons’ Hall, 
Edinburgh, and in the Universities of Edinburgh, Aberdeen, Dublin, 
and in Queen’s College, Belfast. 
Method for Marking Small Objects in Paraffin Imbedding.* — It 
is often difficult, says Herr M. Samter, to discover the whereabouts of a 
small colourless object when imbedded in paraffin ; but this may be 
surmounted by the following device. Paraffin is easily stained red by 
merely rubbing alkanin into it when melted. The object having been 
saturated with this red paraffin, is then imbedded in colourless paraffin 
through which its position is easily discernible. 
Collodium as a Material for Imbedding.f — Prof. G. F. Atkinson 
describes in detail the best method of preparing the various stages in 
the life-history of Ferns, and of using collodium as the imbedding- 
material for sections made with the microtome. 
* Zeitschr. f. wiss. Mikr., xi. (1895) pp. 469-71. 
f ‘ The Study of the Biology of Ferns, &c.,’ New York, 1894, 134 pp. and 
163 figs. See Bot. Centralbl., lxi. (1895) p. 95. 
