34 OF VITAL MOTION. 



until a high degree of inflammatory action is kindled 

 in the part; but if, on the contrary, it be plunged 

 into iced water, the circulation is suspended, and the 

 vessels shrink so completely that the bloodless tissues 

 resemble blanched wax. An effect, in some respects 

 similar, may also be noticed in the skin of persons in 

 whom the circulatory powers are feeble, and the 

 appearance sallow and bloodless during the winter, 

 but who lose their sallowness and become roseate and 

 blooming on the occurrence of summer. In other 

 words it may be said that, in each of these cases, the 

 coats of the vessels expand or contract as heat is 

 imparted or withdrawn. 



So far as we are able to judge, this alteration in 

 capacity would seem to extend to all vessels generally, 

 and to be prolonged in duration, and not to be tran- 

 sient and limited to certain points as in the latici- 

 ferous system of the plant. The exercise of force in 

 this case, as it would appear, is designed to preserve 

 the vessels as open channels, so as to remove as much 

 as possible any resistance which might impede the 

 action of the heart. In the lower grades of exist- 

 ence, however, the case is different, and also in the 

 earlier periods of the foetal history of the higher 

 animals, while the heart is as yet a feeble instrument 

 in the propulsion of the nutrient plasm, for under 

 these circumstances the vessels do actually possess a 

 proper power of movement analogous to the focal 



