410 Proceedings of the British Association. 



in a given time varied with the posture of the individual on 

 whom the observation was made. Dr M'Donnell stated, that 

 this variation of pulse from posture, which he begged leave to 

 call the differential pulse, was not the same in health and dis- 

 ease, being sometimes greater in diseased conditions, and some- 

 times altogether absent; and when absent, that disease is inva- 

 riably present, most probably of the heart or great vessels. One 

 remarkable case was adduced, in which the change from the re- 

 cumbent to the standing posture produced a doubling of the 

 pulse. The pulse of young children is well known to be very 

 rapid ; but that of the foetus Dr M'Donnell stated to be very 

 slow, which becomes doubled at birth. He considered the con- 

 dition of the foetus before birth to be similar to that of cold- 

 blooded animals in its circulation. The objections of stethosco- 

 pists to this, he would say, presented a difficulty, but not fatal 

 to his position, as the rapid beating of the foetal heart, heard 

 through the stethoscope, might proceed from the contractions 

 of the ventricles not being synchronous. That the beating of 

 the heart should be so distinctly heard, though inclosed within 

 the abdomen of the mother, the uterus, membranes, and liquor 

 amnii, would not appear so strange, as it appears at first, from 

 the following experiment : If the faintest-ticking watch be en- 

 closed in an oiled silk bag, and suspended in a vase filled with 

 water, the beating will be heard much more distinctly by the 

 ear applied to the vase than it was whilst the watch was in the 

 open air. Dr M'Donnell adverted to the strength of the pulsa- 

 tion observed, frequently even before birth, in the umbilical 

 cord, and gave an ingenious solution of its cause. In conclu- 

 sion, he made a few observations on the effect of descending or 

 ascending from the surface of the earth ; on the quantity of car- 

 bonic acid exhaled from the lungs ; and, from considerable va- 

 riations in that quantity, without any inconvenience being sus- 

 tained by the individual, he concludes, that the decarboniza- 

 tion of the blood is the least important part of the function of 

 respiration. 



4. The next paper was from Professor Harrison on the small 

 bones found in the hearts of certain ruminantia. He commen- 

 ced with general observations on the circulatory organs, parti- 

 cularly as to their mechanical structure, as suited to the differ- 



