SECT. III.] CONTRACTION OF THE MUSCLES. 415 



department of physiology : I need only mention the prizes 

 offered by the Royal Academy of Prussia,^ and William Croon 

 of London.^ 



Verschuir, in the dissertation already quoted, has attempted 

 to explain the flow of the menses hy this same derivation of the 

 blood, excited every month through the nerves, since this pheno- 

 menon cannot be accounted for either by the theory of a general 

 plethora, which Van Swieten has ah'eady fully refuted in his 

 ' Comments on Boerhaave^s Aphorisms,' or by the notion of a 

 partial uterine plethora. Marherr in particular, following 

 Haller, has attempted to show, that the cause of the flow of the 

 menses is a special plethora of the uterus. He asserts, for 

 instance, that the arteries of the uterus are more capacious and 

 less contractile than the veins, consequently the arteries receive 

 more blood than the veins can return ; that the veins have no 

 valves, and consequently, as the veins cannot so well support 

 the pressure of the blood, its return from the uterus is rendered 

 more difficult ; and thus, from these causes, the blood accumu- 

 lates for a period in the uterine arteries and venous capillaries, 

 until by that time a sufficient quantity being present, it bursts 

 forth. But these distinguished writers do not appear to have 

 considered how much the weight and size of the uterus must be 

 increased every month before the flow of the menses, if it con- 

 tains the whole quantity of blood that is thus discharged. If 

 we estimate its weight at 4, 5, 6, 7, 10, 12 ounces, and this be 

 accumulated in the uterine arteries just before menstruation, the 

 uterus ought at that period to appear manifestly increased in 

 weight and size, a fact which has not been as yet observed or 

 recorded by anatomists. It is thus manifest, that the menstrual 

 blood is not contained in the uterine vessels previously to 

 menstruation, but is derived to the vessels and cavity of the 

 uterus at the time of menstruation, and this by means of the 

 nerves, which seem to be irritated by some stimulus as yet 



• Vide M. Le Cat's ' Dissertation, qui a remporte le prix propose par I'Academie 

 Royale de Prusse, sur le principe de TAction des Muscles/ &c. Berlin, 1753. 



2 Lectures are delivered every year at the College of Physicians of London, on 

 the nature of the muscles and the functions of the nerves, a handsome sum heing 

 bequeathed to the Lecturer. See Thomas Lawrence, * De Natura Musculorum 

 Praelectiones tres in Theatre CoUegii Medicorum Londinensium habitae anno 1759.' 

 Recusje Venetiis, 1766. 



