678 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



foot and body are kept fixed, the general circulation is little or not at 

 all interfered with. The animal may be kept under observation with the 

 Microscope for many hours, without the slightest fall in the blood- 

 pressure resulting. 



As the greatest care in attending to details is necessary in investi- 

 gations such as those in question here, the manner employed for 

 fastening the frogs for examination may be explained. Through the 

 narrow slip of wood upon which the animal rests are cut, near one of 

 its ends, two large holes to allow the passage of the piece of tape 

 which is used to fix the four limbs. The circulation through these is 

 necessarily interfered with to some extent by their being so held, but 

 this it is scarcely possible to avoid without curarizing the animal, and 

 thereby introducing a more serious cause of error. One web having 

 been spread out and fixed by threads to the forked extremity of the 

 holder, the other leg is bent upon itself, as when it is drawn up 

 voluntarily by the animal, in which position it is held by a tape 

 passing loosely round it. It is not difficult so to arrange the tape 

 that it will only press upon the leg when extension is attempted. 

 The leg corresponding to the web which is to be examined is prevented 

 from being drawn up by means of pins stuck into the wood on each 

 side of it. These are placed so that, while they effectually prevent 

 the least flexion, they do not press upon the limb when the latter is at 

 rest. Usually one was placed on the inner side of the ankle, a second 

 on the outer aspect of the knee, and a third on the opposite side of the 

 body close to the pelvis. These are stuck somewhat obliquely into 

 the wood, so that they overhang the part next them, and prevent the 

 leg being raised from the board. In these circumstances frogs will 

 often remain quite motionless for many hours, in a condition more or 

 less closely resembling the so-called " magnetized " state, which can 

 be so readily induced in birds and some other animals. 



When the tongue or mesentery was examined the frogs were 

 curarized. For studying the pressui'e in the vessels of the tail of the 

 fish, a small trough, similar in principle to that recommended by 

 Caton, was used, and in this case an arrangement such as that illus- 

 trated by Fig. 159, but without the paper ring, was employed. 



Rogers' Micrometers. — Prof. W. A. Eogers, of Cambridge, 

 U.S.A. (a Fellow of this Society), having completed his dividing 

 engine, which has been three years in construction, at a cost of ^4000, 

 is willing to furnish standard micrometers without cost to any com- 

 petent person who will make a careful study of the subdivisions, and 

 who will at the same time agree to publish the results, without com- 

 munication with him ; and in order to meet a small portion of the ex- 

 pense incurred in the construction of the machine, he is also prepared 

 to make standards, guaranteed to be aliquot parts, either of the British 

 imperial yard " Bronze 1," or of the " Metre des Archives." 



At present Prof. Eogers will make the following patterns : — 



1. 101 lines -001 inch, and 101 lines -001 cm. with the first line 



in each common to both. 



2. 301 lines, 100 coarse, 100 very fine, for high powers, 101 



coarse, all '01 mm. 



