MOVEMENTS OE RESPIRATION ON THE CIRCULATION OF THE BLOOD. 581 
passage through the breathing-tube. The first of these objections is, I think, answered 
by the tracings. It is seen that in almost every instance they were performed with 
perfect regularity, and that in several they were remarkably slow as compared with the 
ordinary rate of breathing in the dog. Although no anaesthetic was used, yet from 
the simplicity of the operations performed and the rapidity with which they were com- 
pleted, the animals were in a perfectly tranquil condition during the periods of observa- 
tion. Importance is also to be attached to the circumstance that dogs of impure breed 
were always employed. The second objection is of little value ; for it is well known that 
in the tranquil breathing the rhythmical laryngeal movements have no appreciable in- 
fluence on those of the thorax. But the third is of sufficient weight to demand not only 
consideration but special inquiry. 
In preliminary experiments I found that when the caoutchouc bag was connected with 
a mask placed loosely over the animal’s snout, the movements communicated to the lever 
were of the same nature as those represented in the tracings, although of greater extent. 
I had also repeatedly found that the apparatus was so sensible that if the aperture of the 
T tube was placed opposite the nostril at an inch distance, the opposite aperture being 
closed, movements of the lever were produced by the air passing in and out in ordinary 
breathing. By these facts, as well as by the comparison of the width of the T tube with 
that of the natural air-passages, I was convinced that, so far from the resistance afforded 
being greater, it was considerably less than in ordinary breathing through the nostrils. 
Further, from what I believed I had ascertained as to the mode in which the results are 
produced, I was led to expect that they would not have been in the slightest degree mo- 
dified even if the resistance had been many times as great as it actually was. For the 
purpose of testing the truth of this assumption I made the following experiment. 
Observation XII.— June 15th, 1866 (Plate XXIV. figs. 1-4). 
A male brindled mongrel terrier, weighing 30 lbs., was employed. 3T cubic centi- 
metres of a solution of hydrochlorate of morphia, containing one grain per cubic centi-. 
metre, was injected into the cellular tissue of the axilla. The animal became torpid 
almost immediately ; there were no convulsions. The usual operation was then per- 
formed. The connexions having been completed, the clockwork was set in motion 
twenty minutes after the injection of the morphia; the rate of movement of the paper 
being 1 inch in 2 ’9 seconds, and the arterial pressure 5 inches. Observations were con- 
tinued for an hour, during the whole of which period the breathing was regular. The 
T tube which was employed had an internal diameter of four-tenths of an inch ; and in 
order to produce various degrees of resistance cylindrical corks were used, the transverse 
sections of which were reduced by slicing them in planes parallel to their axes, but at 
various distances therefrom. Thus, between the cork and the tube containing it, an 
air-passage was left, of which the section was an arc of a circle of four-tenths of an inch 
in diameter. The corks so prepared were severally marked A, B, C, and D. The form 
of the section of the cork used in the production of each tracing is shown in the 
4x2 
