That the uterine sound is not confined to that part of the uterus where the placenta is attached, as was supposed by Professor Hohl,[43] is proved by the fact that we can frequently hear it in two different and sometimes opposite parts of the uterus at the same time, which, if his opinion be correct, would indicate the presence of twins; and yet the result of labour has proved that the uterus has contained but one child, and that the placenta had neither been attached in the one or other of these situations. The very circumstance which we have already mentioned, of this sound being invariably heard in one, if not in both, of the inguinal regions, shows that it is independent of the vicinity of the placenta; nevertheless, it must be allowed, that as the uterine vessels undergo the greatest degree of development at this part, the sound will usually be at least as distinct here as in any other portion of the uterus. The uterine souffle is the first sound which auscultation detects during pregnancy; it may be heard as early as the fifteenth or sixteenth week, but cases now and then occur where it has been even distinguished in the thirteenth or fourteenth week, and Dr. Evory Kennedy, has given some very interesting examples where he was able to hear it with certainty at the twelfth, eleventh, and even in one instance, at the tenth week. (Kennedy, _op. cit._ p. 80.) During these earlier periods, the sound is weaker, but extends over the whole uterus, from the diminutive size of which it can be heard most readily immediately above the symphysis pubis; in fact, there is every reason to suppose, that the uterine souffle might be detected at a still earlier period, if the uterus were at this time within reach of the stethoscope. As pregnancy advances, it becomes more distinct and powerful, and is occasionally so to a remarkably degree. During the latter periods of pregnancy, it frequently presents considerable modifications of tone, especially where there is general or local vascular excitement, as in cases of fever, or dispositions to hæmorrhage, where the vessels are usually distended, or where (Naegelé, _op. cit._ p. 86,) the placenta is situated near the os uteri, it assumes a piping, twanging sound of considerable resonance: the same is also observed where, either from the weight of the gravid uterus or any other cause, pressure has been exerted on any of the main arterial trunks: hence, as we shall show more fully when speaking of labour, a remarkable change is produced in the tone of the uterine souffle by the first contractions of that process. The causes of these modifications are not always very easily explained; we sometimes observe the souffle on the same side of the uterus vary rapidly in its degree of intensity, and occasionally even disappear for awhile without our being able to assign any satisfactory reason for such changes.