DEEIVATIVE CIRCULATION. 339 



Under stimulation, the muscular fibres in the covering 

 and trabeculse of the corpora cavernosa and spongiosa may 

 contract, force the blood from the parts, and produce a cer- 

 tain amount of rigidity, with diminution in size. This is 

 frequently seen under the influence of cold, which is a pow- 

 erful excitant of the unstriped muscular fibres. 



Derivative Circulation. In some parts of the circulatory 

 system, there exists a direct communication between the arte- 

 ries and the veins, so that all the blood does not necessarily 

 pass through the minute vessels which have been described 

 as true capillaries. This peculiarity has been closely studied 

 by M. Suquet, who was first led to investigate the subject by 

 noticing tnat by injecting a very small quantity of fluid, en- 

 tirely insufficient to fill all the capillaries of a member, it was 

 returned by certain of the veins. On using a black, solidifi- 

 able injection, he found that there were certain parts of the 

 upper and lower extremities arid the head which became 

 colored by the injection, while other parts were not pene- 

 trated. Following this out by dissection, he showed that, in 

 the upper extremity, the skin of the fingers and part of the 

 palm of the hand, and the skin over the olecranon, is provided 

 with vessels of considerable size, which allowed the fluid in- 

 jected by the axillary artery to pass directly into some of 

 the veins, while in other parts the veins were entirely empty. 

 Extending his researches to the lower extremity, he found 

 analogous communications between the vessels in the knee, 

 toes, and parts of the sole of the foot. He also found com- 

 munications in the nose, cheeks, lips, forehead, and ends of 

 the ears, parts which are particularly liable to changes in color 

 from congestion of vessels. 1 



1 J. P. SUQUET, De la Circulation du Sang dans les Membres et dans la Tcte 

 de VHomme, Paris, 1860, p. 55. Though all the physiological deductions in this 

 memoir do not seem justifiable, the anatomical facts are undoubted. The prepa- 

 rations have been examined by a commission, of which M. Robin was a member, 

 which confirmed the statements of M. Suquet. (Oral communication from M. 

 Robin.) 



