402 Dr. Waller on the Origin of Mucus and Pus-globules. 



surface thus appeared to be of a muscular nature. The most 

 ready and correct representation of these diffused stride, is by 

 covering a piece of paper with prints of the papillae of the top 

 of the finger, which has been previously rubbed over with a 

 little printer's ink, in other words, making finger-marks on 

 the paper; when, by drawing parallel lines among these 

 printed papillae, a most faithful image is obtained. 



With regard to other appearances presented by the capil- 

 laries, they will be found described in my former communica- 

 tion. 



Those who have patience to watch for several hours the 

 phaenomena which occur in the capillaries, will perceive the 

 great increase that takes place in the diameters of those under 

 the influence of prolonged irritation, particularly at the edges 

 nearest the irritating agents employed to secure the organ. 

 After watching these changes, it will be seen how slight a cause, 

 such as a temporary obstruction of a vessel by a few globules, 

 is sufficient to determine whether the increase in volume shall 

 be confined to one vessel or be divided among two or more. 

 Therefore we can readily comprehend how the same causes 

 in operation on the embryo may create all those anomalies 

 observed in the distribution of the aortic trunks in the adult, 

 which may be found represented in Bonrgery's plates. 



In endeavouring to account for the fact of the passage of 

 the corpuscles through the vessels we find considerable diffi- 

 culties. It cannot be referred to the influence of vitality, as 

 it is observed likewise to take place after death. It may be 

 surmised, either that the corpuscle, after remaining a certain 

 time in contact with the vessel, gives off by exudation from 

 within itself some substance possessing a solvent power over 

 the vessel, or that the solution of the vessel takes place in 

 virtue of some of those molecular actions which arise from 

 the contact of two bodies ; actions which are now known as 

 exerting such extensive influence in digestion, and are referred 

 to what is termed the catalytic power. 



While advancing these hypotheses we must not omit to bear 

 in mind, that corpuscles are constantly seen adherent, for a 

 long space of time, to the inner sides of a vessel without 

 altering their appearance in the least*. 



Mucus. — In ordinary circumstances, the mucus which is 

 formed on the tongue of the frog contains no particles in sus- 

 pension, but entirely consists of a thick viscous substance, 



* Acetic acid applied to an engorged vessel on the living tongue will 

 dissolve the outer vesicle of the blood-disc and leave the nucleus com- 

 pletely uncovered, in the same way as when the blood is out of the vessels. 

 The action of the acid is almost immediate. 



