290 CIRCULATION. 



in the frog a corpuscle moved at the rate of an inch in ninety 

 seconds. 1 The estimates of Weber and Valentin are con- 

 siderably higher, being about -^ of an inch per second. 

 Yolkmann calculated the rapidity in the mesentery of the 

 dog, which would approximate more nearly to the human 

 subject, and found it to be about -^ of an inch per second. 3 

 Yierordt made a number of curious observations upon him- 

 self, by which he professed to be able to estimate the rapidity 

 of the circulation in the little vessels of the eye. He states 

 that when the eye is fatigued, and sometimes when the ner- 

 vous system is disordered, compression of the globe in a cer- 

 tain way will enable one to see a current like that in a capil- 

 lary plexus. This he believes to be the capillary circulation, 

 and by certain calculations he formed an estimate of its rapid- 

 ity, putting it at from ^ to -fa of an inch. The latter figure 

 accords pretty nearly with the observations of Yolkmann 

 upon the dog. 3 How far these observations are to be relied 

 upon it is impossible to say. Certainly no great importance 

 would be attached to them if they did not, in their results, 

 approximate to the estimates of Yolkmann, which probably 

 represent, more nearly than any, the rapidity in the capil- 

 laries of the human subject. 



After what has been said of the variations in the capillary 

 circulation, it is evident that the foregoing estimates are by 

 no means to be considered exact. 



Relations of the Capillary Circulation to Respiration. 

 In treating of the influence of respiration upon the action of 

 the heart, the arterial pressure, pulse, etc., it has already 

 been stated that non-aerated blood cannot circulate freely in 

 the capillaries. Yarious ideas with regard to the effects of 

 asphyxia upon the circulation have been advanced, which 

 will be again discussed in connection with respiration. The 



1 Statical Exsays, containing Hcemastaticks, London, 1733, p. 68. 



>J MILNE-EDWARDS, Legons sur la Physiologic, Paris, 1869, tome iv., p. 286. 



8 Ibid. 



