LYMPHATIC GLANDS. 439 



could only operate favorably in vessels provided with numer- 

 ous valves. 



We have already referred to the great elasticity of the 

 lymphatics. It is now pretty generally admitted that* the 

 ]arger vessels and those of medium size are also endowed 

 with contractility, though the action of their muscular 

 fibres, like that of all fibres of the involuntary or non-stri- 

 ated variety, is slow and gradual. Todd and Bowman have 

 demonstrated this property by mechanically irritating the 

 thoracic duct in an animal recently killed, but they observed 

 that the contraction was very slow. 1 Milne-Edwards, quot- 

 ing from a manuscript presented by Colin to the Academy of 

 Sciences, in 1858, states that this observer noted alternate 

 filling and emptying of some of the lacteal vessels in the 

 mesentery of the ox ; portions of the vessels becoming alter- 

 nately enlarged in the form of pouches, and contracted so 

 that they almost disappeared. 2 There can be no doubt that 

 the lymphatic vessels possess a certain degree of contractility 

 which is fully as marked, perhaps, as in the venous system. 



Lymphatic Glands. In the course of the lymphatic ves- 

 sels, are found numerous small lenticular bodies, called lym- 

 phatic glands. The number of these glands is very great, 

 though it is estimated with difficulty, from the fact that 

 many of them are very small and are consequently liable 

 to escape observation. It may be stated as an approxi- 

 mation that there are from six to seven hundred lymphatic 

 glands in the body. Their size and form is also very vari- 

 able within the limits of health. They are generally flat- 

 tened and lenticular, some as large as a bean, and others as 

 small as a small pea, or even a pin's head. They are ar- 

 ranged in two sets : one superficial, corresponding with the 

 superficial lymphatic vessels, and a deep set, corresponding 



1 TODD AND BOWMAN, Physiological Anatomy and Physiology of Man, Phila- 

 delphia, 1857, p. 615. 



' MILNE-EDWARDS, Lecons sur la Physiologic, Paris, 1859, tome iv., p. 511. 



