280 Dr. Waller on some Tissues of the Animal Frame, 



We may estimate in some measure the changes which occur 

 in the tongue when under the influence of irritation, by ex- 

 amining it in an animal recently dead, and without its having 

 been subjected to any previous irritation. The capillaries 

 visible are then found to be comparatively very few in number, 

 and less engorged with blood ; but as the blood in this case 

 is perfectly motionless, it is still better to prepare a subject as 

 speedily as possible, when the increase of the number of ca- 

 pillaries may be easily watched. Vessels which before were 

 invisible, are then revealed by the passage of a few particles 

 of blood in a certain defined direction, gradually becoming 

 more distinct. I have never been able to satisfy myself on 

 these occasions of the formation of any new channels for 

 the blood ; on the contrary, they have always appeared to 

 me to be perfectly defined and distinct from the first moment 

 of their appearance. The most remarkable changes to be 

 observed in the tongue are the following : — 



1. Engorgement of the Capillaries. — The capillaries are 

 rapidly injected with blood, which becomes stagnant. Cir- 

 culation is only seen at a few points. The arteries still 

 continue to pour their contents, while the current in the 

 vein becomes more and more languid, until at length it ceases 

 entirely. The vessels appear to contain a red substance, in 

 which we cannot easily detect the separate red particles. 

 The lymph-globules are sometimes seen distinct within the 

 vessels, but they are not generally very abundant : whenever 

 a muscular movement is made, it is found to give rise to a 

 brisk movement of the blood, which continues several instants 

 afterwards. 



2. An increased action in the Capillaries. — The stagna- 

 tion in the capillaries is very slowly produced, for many 

 hours we may witness the admirable sight of these vascular 

 currents moving rapidly in all directions. At one place 

 are the discs, passing through canals sufficiently large to 

 allow several to pass at a time : by tracing this canal to- 

 wards its extremity we find its calibre gradually diminish, 

 until at length the discs or spherules can only pass one at a 

 time. In these vessels may be frequently seen, as it has been 

 described, the state of oscillation of the fluid column, the 

 temporary stagnation of some loop, which is afterwards suc- 

 ceeded by the globules passing with great rapidity, while the 

 adjoining loops in their turn become inactive ; at other times 

 the direction of the current in the loop takes an opposite 

 course, which may continue as long as the examination lasts. 



The most efficient cause in producing these changes in the 

 capillary circulation is, without doubt, muscular contraction; 

 for whenever that occurs, a state of great activity is produced 



