On Diapedesis. 81 



projecting cork, above the hole, partly covering its surface. An 

 incision is made parallel to the median line on the right side of the 

 belly. Care must be taken not to sever any large vessels. A 

 similar incision is then made in the exposed muscles, still avoiding 

 the blood-vessels. Should there be any bleeding from a large vessel 

 it must be restrained by torsion or ligature. All traces of blood 

 having been removed with bibulous paper, the intestines and 

 mesentery are drawn out carefully and placed on the projecting 

 cork. The animal must lie supine. The intestine is covered with 

 bibulous paper, and a thin " cover " glass placed on the mesentery. 

 The whole is kept moist by the frequent addition of a few drops of 

 a \ per cent, solution of chloride of sodium. The mesentery should 

 be exposed for two or three hours before required for observation. 



3. The tongue was first used by Cohnheim. The animal in 

 this experiment must also be curarized. A plate, similar to that 

 last described, is used. The tongue is drawn out and ligatured 

 near its root. Forty-eight hours after, the ligature is removed, and 

 the circulation generally recovers in a short time. Dr. Mitchell 

 Bruce suggests interposing a piece of leather between the ligature 

 and the tongue, to prevent injury to the organ. The animal is 

 placed on its back, the tongue drawn forwards, spread over the thin 

 glass, and secured in position by means of small pins. The dorsum 

 of the organ will be directed upwards. 



4. The tail of the tadpole can be arranged with great facility, 

 and affords a most interesting object. Dr. Klein recommends 

 curarizing the animal by placing it in a moderately strong solution 

 of curara until motionless. It is then placed on an ordinary glass 

 slip, the tail covered with a thin glass, and kept moist by the 

 addition of salt solution when necessary. 



II. The examination should be commenced with a low power, 

 so that a moderate-sized vein can be easily selected. The low 

 power is changed for a No. 7 Hartnack, corresponding to an 

 Enghsh quarter inch. The chosen vessel must now be closely 

 watched. 



In every vessel, so long as the parts are natural, the central 

 part of the current is occupied by coloured, and the periphery by 

 colourless, corpuscles. The coloured pass along with their long 

 axes parallel to the long axis of the vessel, whilst the colourless 

 assume a spheroidal form, and move more slowly, or, as Dr. Burdon 

 Sanderson has aptly likened them, to " round pebbles in a shallow 

 but rapid stream." 



A column of fluid may be supposed to consist of several strata, 

 and the friction of the fluid against the wall of the vessel causes 

 the external layer to move more slowly ; hence the slow onward 

 progress of the colourless, and the quicker transit of the coloured. 

 After a while the relation will be seen to be altered; the vessel 



