GENERAL RAPIDITY. 345 



The experiments of Hering were evidently conducted with 

 great care and accuracy. He drew the blood at intervals of 

 five seconds after the commencement of the injection, and 

 thus, by repeated observations, ascertained pretty nearly the 

 rapidity of a circuit of blood in the animals on which he ex- 

 perimented. Others have taken up these investigations, and 

 introduced some modifications in the manipulations. Vier- 

 ordt collected the blood as it flowed, in little vessels fixed on 

 a disk revolving at a known rate, which gave a little more 

 exactness to the observations ; 1 but the method is essentially 

 the same as that employed by Hering, and the results obtain- 

 ed by these two observers nearly correspond. 



The length of time occupied by a portion of blood in 

 making a complete circuit of the vascular system, in the hu- 

 man subject, is only to be deduced from observations on the 

 inferior animals ; but before this application is made, it will 

 be well to examine the objections, if any exist, to the experi- 

 mental procedure above described. 



The only objection which could be made is, that a saline 

 solution, introduced into the torrent of the circulation, would 

 have a tendency to diffuse itself throughout the whole mass 

 of blood, it might be, with considerable rapidity ; ancj that 

 this fact is opposed to the proposition that the salt, when de- 

 tected in a specimen of blood drawn from a given vessel, is 

 simply carried there by the force of the blood-current. This 

 objection to the observations of Hering has been made, by 

 Matteucci, and is considered by him as fatal to their accu- 

 racy. 3 It certainly is an element which should be taken into 

 account ; but from the definite data which have been ob- 

 tained concerning the rapidity of the arterial circulation, and 

 the inferences which are unavoidable with regard to the ra- 

 pidity of the venous circulation, it would seem that the saline 

 solution must be carried on by the mere rapidity of the arte- 

 rial flow to the capillaries, which are very short, taken up 



1 MILNE-EDWARDS, loc. cit. 



2 MATTEUCCI, Phenomenes Physiques des Corps Vivants, p. 326 et scq. 



