346 Dr. Poiseuille, on the 



of the temperature of the whole mass of blood being sunk. 

 The ice in the vessel was replaced by water at the tempera- 

 ture 100°, and the velocity of the globules became then so 

 great, that their form could scarcely be distinguished. In 

 young rats, the cold, applied only for a few minutes, 

 stopped the circulation in the capillaries of the mesentery. 

 It gradually resumed its powers, and accpaired its normal 

 rhythm after the ice was withdrawn. 



Thus the diminished velocity of the capillary circulation 

 by cold, and its greater rapidity by the action of cold, are 

 naturally interpreted by the increase in the thickness of this 

 layer in the first place, and its diminution in the second. 



These results completely correspond with those of M. 

 Girard on the variation in the thickness of the layer which 

 lines the coats of inert tubes, when the temperature 

 increases or diminishes. 



We know that certain animals, such as fishes, and some 

 amphibious mammalia, are sometimes immersed nearly 

 262£ feet (80 metres) beneath the surface of the water, and 

 then support a pressure of from seven to eight atmospheres. 

 It is important, therefore, to know how this layer acts, and 

 at the same time to observe the modifications of the capil- 

 lary circulation under such pressure. With this object in 

 view, the author has constructed an apparatus, to which he 

 has given the name of Porte-objet pneumatique. A short 

 description will afford an idea of it, and develope the 

 results which may be derived from its use. It consists of a 

 strong box of copper ; the top and bottom are formed of 

 crystal, fitted into grooves placed in the sides. One of the 

 extremities of this box carries a copper tube, which contains 

 sometimes a barometer tube, and sometimes a manometer 

 for compressed air ; the other extremity presents a large 

 opening by which the animals are introduced. To this 

 extremity sometimes a suction pump is adapted, and some- 

 times a forcing pump. The animal, prepared in such a 

 way as to allow the capillary circulation to be seen, is 

 placed in the instrument, and the apparatus placed under 

 the microscope. We can then observe the modifications 

 which may introduce in the capillary circulation a more or 

 less considerable pressure. In salamanders, frogs, tad- 

 poles, young rats and mice, the arterial, venous, and capil- 



