14G The Microscope. 



the vessels will presently become much paler, because 

 the arrested blood will have recommenced its progress. 

 When the web is magnified about thirty-five 

 diameters, it affords a most curious spectacle. The 

 largest web in fig. 3 contained two principal veins 

 and an artery. This latter crossed the web where 

 the letter a is marked; it ran with amazing 

 rapidity in its broader parts, but at length ramified 

 into capiP^ies, and slackened its pace. The two 

 veins moved much more slowly. They were well sup- 

 plied in their centres with corpuscles from the capil- 

 laries, and each vein flowed from about the centre of 

 the web towards the large veins placed above to the 

 frog's third and fourth toe. Thus the sinuous vein to 

 the left of a flowed downwards from a point parallel 

 to a, and upwards in a contrary direction; but I 

 noticed that the point of separation was not uniformly 

 in the same spot. 



When a portion of the web is viewed with a 

 power of 100 diameters, it becomes evident that some 

 of the capillaries lie near the surface of the web 

 some deeper in its substance, and some close to the 

 under surface. Some of these latter again, often 

 seem to find their way suddenly to the upper surface, 

 and cross over and under others without communi- 

 cating with them. Some of them are very small and 

 sparingly supplied with corpuscles; and these are 

 only visible occasionally when their existence is shown 

 by two or three stray corpuscles passing through 

 them. The substance of the web is not perfectly, 

 transparent, and seems, when the microscope is at the 



